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From:   Nhat Pham <nphamcs@gmail.com>
Date:   Fri, 14 Jul 2023 15:25:54 -0700
Message-ID: <CAKEwX=PB=q_Y=QtemFwrLAGxco1arfUrFfnqgYgP+vDHmOyMvA@mail.gmail.com>
Subject: Re: [PATCH] mm: kill frontswap
To:     Johannes Weiner <hannes@cmpxchg.org>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Yosry Ahmed <yosryahmed@google.com>,
        Christoph Hellwig <hch@infradead.org>,
        Domenico Cerasuolo <cerasuolodomenico@gmail.com>,
        konrad.wilk@oracle.com, vitaly.wool@konsulko.com,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
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On Fri, Jul 14, 2023 at 12:46=E2=80=AFPM Johannes Weiner <hannes@cmpxchg.or=
g> wrote:
>
> The only user of frontswap is zswap, and has been for a long
> time. Have swap call into zswap directly and remove the indirection.
>
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
> ---
>  Documentation/admin-guide/mm/zswap.rst        |  14 +-
>  Documentation/mm/frontswap.rst                | 264 ----------------
>  Documentation/mm/index.rst                    |   1 -
>  .../translations/zh_CN/mm/frontswap.rst       | 196 ------------
>  Documentation/translations/zh_CN/mm/index.rst |   1 -
>  MAINTAINERS                                   |   7 -
>  fs/proc/meminfo.c                             |   1 +
>  include/linux/frontswap.h                     |  91 ------
>  include/linux/swap.h                          |   9 -
>  include/linux/swapfile.h                      |   5 -
>  include/linux/zswap.h                         |  37 +++
>  mm/Kconfig                                    |   4 -
>  mm/Makefile                                   |   1 -
>  mm/frontswap.c                                | 283 ------------------
>  mm/page_io.c                                  |   6 +-
>  mm/swapfile.c                                 |  33 +-
>  mm/zswap.c                                    | 157 ++++------
>  17 files changed, 121 insertions(+), 989 deletions(-)
>  delete mode 100644 Documentation/mm/frontswap.rst
>  delete mode 100644 Documentation/translations/zh_CN/mm/frontswap.rst
>  delete mode 100644 include/linux/frontswap.h
>  create mode 100644 include/linux/zswap.h
>  delete mode 100644 mm/frontswap.c
>
> diff --git a/Documentation/admin-guide/mm/zswap.rst b/Documentation/admin=
-guide/mm/zswap.rst
> index c5c2c7dbb155..45b98390e938 100644
> --- a/Documentation/admin-guide/mm/zswap.rst
> +++ b/Documentation/admin-guide/mm/zswap.rst
> @@ -49,7 +49,7 @@ compressed pool.
>  Design
>  =3D=3D=3D=3D=3D=3D
>
> -Zswap receives pages for compression through the Frontswap API and is ab=
le to
> +Zswap receives pages for compression from the swap subsystem and is able=
 to
>  evict pages from its own compressed pool on an LRU basis and write them =
back to
>  the backing swap device in the case that the compressed pool is full.
>
> @@ -70,19 +70,19 @@ means the compression ratio will always be 2:1 or wor=
se (because of half-full
>  zbud pages).  The zsmalloc type zpool has a more complex compressed page
>  storage method, and it can achieve greater storage densities.
>
> -When a swap page is passed from frontswap to zswap, zswap maintains a ma=
pping
> +When a swap page is passed from swapout to zswap, zswap maintains a mapp=
ing
>  of the swap entry, a combination of the swap type and swap offset, to th=
e zpool
>  handle that references that compressed swap page.  This mapping is achie=
ved
>  with a red-black tree per swap type.  The swap offset is the search key =
for the
>  tree nodes.
>
> -During a page fault on a PTE that is a swap entry, frontswap calls the z=
swap
> -load function to decompress the page into the page allocated by the page=
 fault
> -handler.
> +During a page fault on a PTE that is a swap entry, the swapin code calls=
 the
> +zswap load function to decompress the page into the page allocated by th=
e page
> +fault handler.
>
>  Once there are no PTEs referencing a swap page stored in zswap (i.e. the=
 count
> -in the swap_map goes to 0) the swap code calls the zswap invalidate func=
tion,
> -via frontswap, to free the compressed entry.
> +in the swap_map goes to 0) the swap code calls the zswap invalidate func=
tion
> +to free the compressed entry.
>
>  Zswap seeks to be simple in its policies.  Sysfs attributes allow for on=
e user
>  controlled policy:
> diff --git a/Documentation/mm/frontswap.rst b/Documentation/mm/frontswap.=
rst
> deleted file mode 100644
> index c892412988af..000000000000
> --- a/Documentation/mm/frontswap.rst
> +++ /dev/null
> @@ -1,264 +0,0 @@
> -=3D=3D=3D=3D=3D=3D=3D=3D=3D
> -Frontswap
> -=3D=3D=3D=3D=3D=3D=3D=3D=3D
> -
> -Frontswap provides a "transcendent memory" interface for swap pages.
> -In some environments, dramatic performance savings may be obtained becau=
se
> -swapped pages are saved in RAM (or a RAM-like device) instead of a swap =
disk.
> -
> -.. _Transcendent memory in a nutshell: https://lwn.net/Articles/454795/
> -
> -Frontswap is so named because it can be thought of as the opposite of
> -a "backing" store for a swap device.  The storage is assumed to be
> -a synchronous concurrency-safe page-oriented "pseudo-RAM device" conform=
ing
> -to the requirements of transcendent memory (such as Xen's "tmem", or
> -in-kernel compressed memory, aka "zcache", or future RAM-like devices);
> -this pseudo-RAM device is not directly accessible or addressable by the
> -kernel and is of unknown and possibly time-varying size.  The driver
> -links itself to frontswap by calling frontswap_register_ops to set the
> -frontswap_ops funcs appropriately and the functions it provides must
> -conform to certain policies as follows:
> -
> -An "init" prepares the device to receive frontswap pages associated
> -with the specified swap device number (aka "type").  A "store" will
> -copy the page to transcendent memory and associate it with the type and
> -offset associated with the page. A "load" will copy the page, if found,
> -from transcendent memory into kernel memory, but will NOT remove the pag=
e
> -from transcendent memory.  An "invalidate_page" will remove the page
> -from transcendent memory and an "invalidate_area" will remove ALL pages
> -associated with the swap type (e.g., like swapoff) and notify the "devic=
e"
> -to refuse further stores with that swap type.
> -
> -Once a page is successfully stored, a matching load on the page will nor=
mally
> -succeed.  So when the kernel finds itself in a situation where it needs
> -to swap out a page, it first attempts to use frontswap.  If the store re=
turns
> -success, the data has been successfully saved to transcendent memory and
> -a disk write and, if the data is later read back, a disk read are avoide=
d.
> -If a store returns failure, transcendent memory has rejected the data, a=
nd the
> -page can be written to swap as usual.
> -
> -Note that if a page is stored and the page already exists in transcenden=
t memory
> -(a "duplicate" store), either the store succeeds and the data is overwri=
tten,
> -or the store fails AND the page is invalidated.  This ensures stale data=
 may
> -never be obtained from frontswap.
> -
> -If properly configured, monitoring of frontswap is done via debugfs in
> -the `/sys/kernel/debug/frontswap` directory.  The effectiveness of
> -frontswap can be measured (across all swap devices) with:
> -
> -``failed_stores``
> -       how many store attempts have failed
> -
> -``loads``
> -       how many loads were attempted (all should succeed)
> -
> -``succ_stores``
> -       how many store attempts have succeeded
> -
> -``invalidates``
> -       how many invalidates were attempted
> -
> -A backend implementation may provide additional metrics.
> -
> -FAQ
> -=3D=3D=3D
> -
> -* Where's the value?
> -
> -When a workload starts swapping, performance falls through the floor.
> -Frontswap significantly increases performance in many such workloads by
> -providing a clean, dynamic interface to read and write swap pages to
> -"transcendent memory" that is otherwise not directly addressable to the =
kernel.
> -This interface is ideal when data is transformed to a different form
> -and size (such as with compression) or secretly moved (as might be
> -useful for write-balancing for some RAM-like devices).  Swap pages (and
> -evicted page-cache pages) are a great use for this kind of slower-than-R=
AM-
> -but-much-faster-than-disk "pseudo-RAM device".
> -
> -Frontswap with a fairly small impact on the kernel,
> -provides a huge amount of flexibility for more dynamic, flexible RAM
> -utilization in various system configurations:
> -
> -In the single kernel case, aka "zcache", pages are compressed and
> -stored in local memory, thus increasing the total anonymous pages
> -that can be safely kept in RAM.  Zcache essentially trades off CPU
> -cycles used in compression/decompression for better memory utilization.
> -Benchmarks have shown little or no impact when memory pressure is
> -low while providing a significant performance improvement (25%+)
> -on some workloads under high memory pressure.
> -
> -"RAMster" builds on zcache by adding "peer-to-peer" transcendent memory
> -support for clustered systems.  Frontswap pages are locally compressed
> -as in zcache, but then "remotified" to another system's RAM.  This
> -allows RAM to be dynamically load-balanced back-and-forth as needed,
> -i.e. when system A is overcommitted, it can swap to system B, and
> -vice versa.  RAMster can also be configured as a memory server so
> -many servers in a cluster can swap, dynamically as needed, to a single
> -server configured with a large amount of RAM... without pre-configuring
> -how much of the RAM is available for each of the clients!
> -
> -In the virtual case, the whole point of virtualization is to statistical=
ly
> -multiplex physical resources across the varying demands of multiple
> -virtual machines.  This is really hard to do with RAM and efforts to do
> -it well with no kernel changes have essentially failed (except in some
> -well-publicized special-case workloads).
> -Specifically, the Xen Transcendent Memory backend allows otherwise
> -"fallow" hypervisor-owned RAM to not only be "time-shared" between multi=
ple
> -virtual machines, but the pages can be compressed and deduplicated to
> -optimize RAM utilization.  And when guest OS's are induced to surrender
> -underutilized RAM (e.g. with "selfballooning"), sudden unexpected
> -memory pressure may result in swapping; frontswap allows those pages
> -to be swapped to and from hypervisor RAM (if overall host system memory
> -conditions allow), thus mitigating the potentially awful performance imp=
act
> -of unplanned swapping.
> -
> -A KVM implementation is underway and has been RFC'ed to lkml.  And,
> -using frontswap, investigation is also underway on the use of NVM as
> -a memory extension technology.
> -
> -* Sure there may be performance advantages in some situations, but
> -  what's the space/time overhead of frontswap?
> -
> -If CONFIG_FRONTSWAP is disabled, every frontswap hook compiles into
> -nothingness and the only overhead is a few extra bytes per swapon'ed
> -swap device.  If CONFIG_FRONTSWAP is enabled but no frontswap "backend"
> -registers, there is one extra global variable compared to zero for
> -every swap page read or written.  If CONFIG_FRONTSWAP is enabled
> -AND a frontswap backend registers AND the backend fails every "store"
> -request (i.e. provides no memory despite claiming it might),
> -CPU overhead is still negligible -- and since every frontswap fail
> -precedes a swap page write-to-disk, the system is highly likely
> -to be I/O bound and using a small fraction of a percent of a CPU
> -will be irrelevant anyway.
> -
> -As for space, if CONFIG_FRONTSWAP is enabled AND a frontswap backend
> -registers, one bit is allocated for every swap page for every swap
> -device that is swapon'd.  This is added to the EIGHT bits (which
> -was sixteen until about 2.6.34) that the kernel already allocates
> -for every swap page for every swap device that is swapon'd.  (Hugh
> -Dickins has observed that frontswap could probably steal one of
> -the existing eight bits, but let's worry about that minor optimization
> -later.)  For very large swap disks (which are rare) on a standard
> -4K pagesize, this is 1MB per 32GB swap.
> -
> -When swap pages are stored in transcendent memory instead of written
> -out to disk, there is a side effect that this may create more memory
> -pressure that can potentially outweigh the other advantages.  A
> -backend, such as zcache, must implement policies to carefully (but
> -dynamically) manage memory limits to ensure this doesn't happen.
> -
> -* OK, how about a quick overview of what this frontswap patch does
> -  in terms that a kernel hacker can grok?
> -
> -Let's assume that a frontswap "backend" has registered during
> -kernel initialization; this registration indicates that this
> -frontswap backend has access to some "memory" that is not directly
> -accessible by the kernel.  Exactly how much memory it provides is
> -entirely dynamic and random.
> -
> -Whenever a swap-device is swapon'd frontswap_init() is called,
> -passing the swap device number (aka "type") as a parameter.
> -This notifies frontswap to expect attempts to "store" swap pages
> -associated with that number.
> -
> -Whenever the swap subsystem is readying a page to write to a swap
> -device (c.f swap_writepage()), frontswap_store is called.  Frontswap
> -consults with the frontswap backend and if the backend says it does NOT
> -have room, frontswap_store returns -1 and the kernel swaps the page
> -to the swap device as normal.  Note that the response from the frontswap
> -backend is unpredictable to the kernel; it may choose to never accept a
> -page, it could accept every ninth page, or it might accept every
> -page.  But if the backend does accept a page, the data from the page
> -has already been copied and associated with the type and offset,
> -and the backend guarantees the persistence of the data.  In this case,
> -frontswap sets a bit in the "frontswap_map" for the swap device
> -corresponding to the page offset on the swap device to which it would
> -otherwise have written the data.
> -
> -When the swap subsystem needs to swap-in a page (swap_readpage()),
> -it first calls frontswap_load() which checks the frontswap_map to
> -see if the page was earlier accepted by the frontswap backend.  If
> -it was, the page of data is filled from the frontswap backend and
> -the swap-in is complete.  If not, the normal swap-in code is
> -executed to obtain the page of data from the real swap device.
> -
> -So every time the frontswap backend accepts a page, a swap device read
> -and (potentially) a swap device write are replaced by a "frontswap backe=
nd
> -store" and (possibly) a "frontswap backend loads", which are presumably =
much
> -faster.
> -
> -* Can't frontswap be configured as a "special" swap device that is
> -  just higher priority than any real swap device (e.g. like zswap,
> -  or maybe swap-over-nbd/NFS)?
> -
> -No.  First, the existing swap subsystem doesn't allow for any kind of
> -swap hierarchy.  Perhaps it could be rewritten to accommodate a hierarch=
y,
> -but this would require fairly drastic changes.  Even if it were
> -rewritten, the existing swap subsystem uses the block I/O layer which
> -assumes a swap device is fixed size and any page in it is linearly
> -addressable.  Frontswap barely touches the existing swap subsystem,
> -and works around the constraints of the block I/O subsystem to provide
> -a great deal of flexibility and dynamicity.
> -
> -For example, the acceptance of any swap page by the frontswap backend is
> -entirely unpredictable. This is critical to the definition of frontswap
> -backends because it grants completely dynamic discretion to the
> -backend.  In zcache, one cannot know a priori how compressible a page is=
.
> -"Poorly" compressible pages can be rejected, and "poorly" can itself be
> -defined dynamically depending on current memory constraints.
> -
> -Further, frontswap is entirely synchronous whereas a real swap
> -device is, by definition, asynchronous and uses block I/O.  The
> -block I/O layer is not only unnecessary, but may perform "optimizations"
> -that are inappropriate for a RAM-oriented device including delaying
> -the write of some pages for a significant amount of time.  Synchrony is
> -required to ensure the dynamicity of the backend and to avoid thorny rac=
e
> -conditions that would unnecessarily and greatly complicate frontswap
> -and/or the block I/O subsystem.  That said, only the initial "store"
> -and "load" operations need be synchronous.  A separate asynchronous thre=
ad
> -is free to manipulate the pages stored by frontswap.  For example,
> -the "remotification" thread in RAMster uses standard asynchronous
> -kernel sockets to move compressed frontswap pages to a remote machine.
> -Similarly, a KVM guest-side implementation could do in-guest compression
> -and use "batched" hypercalls.
> -
> -In a virtualized environment, the dynamicity allows the hypervisor
> -(or host OS) to do "intelligent overcommit".  For example, it can
> -choose to accept pages only until host-swapping might be imminent,
> -then force guests to do their own swapping.
> -
> -There is a downside to the transcendent memory specifications for
> -frontswap:  Since any "store" might fail, there must always be a real
> -slot on a real swap device to swap the page.  Thus frontswap must be
> -implemented as a "shadow" to every swapon'd device with the potential
> -capability of holding every page that the swap device might have held
> -and the possibility that it might hold no pages at all.  This means
> -that frontswap cannot contain more pages than the total of swapon'd
> -swap devices.  For example, if NO swap device is configured on some
> -installation, frontswap is useless.  Swapless portable devices
> -can still use frontswap but a backend for such devices must configure
> -some kind of "ghost" swap device and ensure that it is never used.
> -
> -* Why this weird definition about "duplicate stores"?  If a page
> -  has been previously successfully stored, can't it always be
> -  successfully overwritten?
> -
> -Nearly always it can, but no, sometimes it cannot.  Consider an example
> -where data is compressed and the original 4K page has been compressed
> -to 1K.  Now an attempt is made to overwrite the page with data that
> -is non-compressible and so would take the entire 4K.  But the backend
> -has no more space.  In this case, the store must be rejected.  Whenever
> -frontswap rejects a store that would overwrite, it also must invalidate
> -the old data and ensure that it is no longer accessible.  Since the
> -swap subsystem then writes the new data to the read swap device,
> -this is the correct course of action to ensure coherency.
> -
> -* Why does the frontswap patch create the new include file swapfile.h?
> -
> -The frontswap code depends on some swap-subsystem-internal data
> -structures that have, over the years, moved back and forth between
> -static and global.  This seemed a reasonable compromise:  Define
> -them as global but declare them in a new include file that isn't
> -included by the large number of source files that include swap.h.
> -
> -Dan Magenheimer, last updated April 9, 2012
> diff --git a/Documentation/mm/index.rst b/Documentation/mm/index.rst
> index 5a94a921ea40..31d2ac306438 100644
> --- a/Documentation/mm/index.rst
> +++ b/Documentation/mm/index.rst
> @@ -44,7 +44,6 @@ above structured documentation, or deleted if it has se=
rved its purpose.
>     balance
>     damon/index
>     free_page_reporting
> -   frontswap
>     hmm
>     hwpoison
>     hugetlbfs_reserv
> diff --git a/Documentation/translations/zh_CN/mm/frontswap.rst b/Document=
ation/translations/zh_CN/mm/frontswap.rst
> deleted file mode 100644
> index 434975390b48..000000000000
> --- a/Documentation/translations/zh_CN/mm/frontswap.rst
> +++ /dev/null
> @@ -1,196 +0,0 @@
> -:Original: Documentation/mm/frontswap.rst
> -
> -:=E7=BF=BB=E8=AF=91:
> -
> - =E5=8F=B8=E5=BB=B6=E8=85=BE Yanteng Si <siyanteng@loongson.cn>
> -
> -:=E6=A0=A1=E8=AF=91:
> -
> -=3D=3D=3D=3D=3D=3D=3D=3D=3D
> -Frontswap
> -=3D=3D=3D=3D=3D=3D=3D=3D=3D
> -
> -Frontswap=E4=B8=BA=E4=BA=A4=E6=8D=A2=E9=A1=B5=E6=8F=90=E4=BE=9B=E4=BA=86=
=E4=B8=80=E4=B8=AA =E2=80=9Ctranscendent memory=E2=80=9D =E7=9A=84=E6=8E=A5=
=E5=8F=A3=E3=80=82=E5=9C=A8=E4=B8=80=E4=BA=9B=E7=8E=AF=E5=A2=83=E4=B8=AD=EF=
=BC=8C=E7=94=B1
> -=E4=BA=8E=E4=BA=A4=E6=8D=A2=E9=A1=B5=E8=A2=AB=E4=BF=9D=E5=AD=98=E5=9C=A8=
RAM=EF=BC=88=E6=88=96=E7=B1=BB=E4=BC=BCRAM=E7=9A=84=E8=AE=BE=E5=A4=87=EF=BC=
=89=E4=B8=AD=EF=BC=8C=E8=80=8C=E4=B8=8D=E6=98=AF=E4=BA=A4=E6=8D=A2=E7=A3=81=
=E7=9B=98=EF=BC=8C=E5=9B=A0=E6=AD=A4=E5=8F=AF=E4=BB=A5=E8=8E=B7=E5=BE=97=E5=
=B7=A8=E5=A4=A7=E7=9A=84=E6=80=A7=E8=83=BD
> -=E8=8A=82=E7=9C=81=EF=BC=88=E6=8F=90=E9=AB=98=EF=BC=89=E3=80=82
> -
> -.. _Transcendent memory in a nutshell: https://lwn.net/Articles/454795/
> -
> -Frontswap=E4=B9=8B=E6=89=80=E4=BB=A5=E8=BF=99=E4=B9=88=E5=91=BD=E5=90=8D=
=EF=BC=8C=E6=98=AF=E5=9B=A0=E4=B8=BA=E5=AE=83=E5=8F=AF=E4=BB=A5=E8=A2=AB=E8=
=AE=A4=E4=B8=BA=E6=98=AF=E4=B8=8Eswap=E8=AE=BE=E5=A4=87=E7=9A=84=E2=80=9Cba=
ck=E2=80=9D=E5=AD=98=E5=82=A8=E7=9B=B8=E5=8F=8D=E3=80=82=E5=AD=98
> -=E5=82=A8=E5=99=A8=E8=A2=AB=E8=AE=A4=E4=B8=BA=E6=98=AF=E4=B8=80=E4=B8=AA=
=E5=90=8C=E6=AD=A5=E5=B9=B6=E5=8F=91=E5=AE=89=E5=85=A8=E7=9A=84=E9=9D=A2=E5=
=90=91=E9=A1=B5=E9=9D=A2=E7=9A=84=E2=80=9C=E4=BC=AARAM=E8=AE=BE=E5=A4=87=E2=
=80=9D=EF=BC=8C=E7=AC=A6=E5=90=88transcendent memory
> -=EF=BC=88=E5=A6=82Xen=E7=9A=84=E2=80=9Ctmem=E2=80=9D=EF=BC=8C=E6=88=96=
=E5=86=85=E6=A0=B8=E5=86=85=E5=8E=8B=E7=BC=A9=E5=86=85=E5=AD=98=EF=BC=8C=E5=
=8F=88=E7=A7=B0=E2=80=9Czcache=E2=80=9D=EF=BC=8C=E6=88=96=E6=9C=AA=E6=9D=A5=
=E7=9A=84=E7=B1=BB=E4=BC=BCRAM=E7=9A=84=E8=AE=BE=E5=A4=87=EF=BC=89=E7=9A=84=
=E8=A6=81
> -=E6=B1=82=EF=BC=9B=E8=BF=99=E4=B8=AA=E4=BC=AARAM=E8=AE=BE=E5=A4=87=E4=B8=
=8D=E8=83=BD=E8=A2=AB=E5=86=85=E6=A0=B8=E7=9B=B4=E6=8E=A5=E8=AE=BF=E9=97=AE=
=E6=88=96=E5=AF=BB=E5=9D=80=EF=BC=8C=E5=85=B6=E5=A4=A7=E5=B0=8F=E6=9C=AA=E7=
=9F=A5=E4=B8=94=E5=8F=AF=E8=83=BD=E9=9A=8F=E6=97=B6=E9=97=B4=E5=8F=98=E5=8C=
=96=E3=80=82=E9=A9=B1=E5=8A=A8=E7=A8=8B=E5=BA=8F=E9=80=9A=E8=BF=87
> -=E8=B0=83=E7=94=A8frontswap_register_ops=E5=B0=86=E8=87=AA=E5=B7=B1=E4=
=B8=8Efrontswap=E9=93=BE=E6=8E=A5=E8=B5=B7=E6=9D=A5=EF=BC=8C=E4=BB=A5=E9=80=
=82=E5=BD=93=E5=9C=B0=E8=AE=BE=E7=BD=AEfrontswap_ops
> -=E7=9A=84=E5=8A=9F=E8=83=BD=EF=BC=8C=E5=AE=83=E6=8F=90=E4=BE=9B=E7=9A=84=
=E5=8A=9F=E8=83=BD=E5=BF=85=E9=A1=BB=E7=AC=A6=E5=90=88=E6=9F=90=E4=BA=9B=E7=
=AD=96=E7=95=A5=EF=BC=8C=E5=A6=82=E4=B8=8B=E6=89=80=E7=A4=BA:
> -
> -=E4=B8=80=E4=B8=AA =E2=80=9Cinit=E2=80=9D =E5=B0=86=E8=AE=BE=E5=A4=87=E5=
=87=86=E5=A4=87=E5=A5=BD=E6=8E=A5=E6=94=B6=E4=B8=8E=E6=8C=87=E5=AE=9A=E7=9A=
=84=E4=BA=A4=E6=8D=A2=E8=AE=BE=E5=A4=87=E7=BC=96=E5=8F=B7=EF=BC=88=E5=8F=88=
=E7=A7=B0=E2=80=9C=E7=B1=BB=E5=9E=8B=E2=80=9D=EF=BC=89=E7=9B=B8=E5=85=B3=E7=
=9A=84frontswap
> -=E4=BA=A4=E6=8D=A2=E9=A1=B5=E3=80=82=E4=B8=80=E4=B8=AA =E2=80=9Cstore=E2=
=80=9D =E5=B0=86=E6=8A=8A=E8=AF=A5=E9=A1=B5=E5=A4=8D=E5=88=B6=E5=88=B0trans=
cendent memory=EF=BC=8C=E5=B9=B6=E4=B8=8E=E8=AF=A5=E9=A1=B5=E7=9A=84=E7=B1=
=BB=E5=9E=8B=E5=92=8C=E5=81=8F=E7=A7=BB
> -=E9=87=8F=E7=9B=B8=E5=85=B3=E8=81=94=E3=80=82=E4=B8=80=E4=B8=AA =E2=80=
=9Cload=E2=80=9D =E5=B0=86=E6=8A=8A=E8=AF=A5=E9=A1=B5=EF=BC=8C=E5=A6=82=E6=
=9E=9C=E6=89=BE=E5=88=B0=E7=9A=84=E8=AF=9D=EF=BC=8C=E4=BB=8Etranscendent me=
mory=E5=A4=8D=E5=88=B6=E5=88=B0=E5=86=85=E6=A0=B8
> -=E5=86=85=E5=AD=98=EF=BC=8C=E4=BD=86=E4=B8=8D=E4=BC=9A=E4=BB=8Etranscend=
ent memory=E4=B8=AD=E5=88=A0=E9=99=A4=E8=AF=A5=E9=A1=B5=E3=80=82=E4=B8=80=
=E4=B8=AA =E2=80=9Cinvalidate_page=E2=80=9D =E5=B0=86=E4=BB=8E
> -transcendent memory=E4=B8=AD=E5=88=A0=E9=99=A4=E8=AF=A5=E9=A1=B5=EF=BC=
=8C=E4=B8=80=E4=B8=AA =E2=80=9Cinvalidate_area=E2=80=9D =E5=B0=86=E5=88=A0=
=E9=99=A4=E6=89=80=E6=9C=89=E4=B8=8E=E4=BA=A4=E6=8D=A2=E7=B1=BB=E5=9E=8B
> -=E7=9B=B8=E5=85=B3=E7=9A=84=E9=A1=B5=EF=BC=88=E4=BE=8B=E5=A6=82=EF=BC=8C=
=E5=83=8Fswapoff=EF=BC=89=E5=B9=B6=E9=80=9A=E7=9F=A5 =E2=80=9Cdevice=E2=80=
=9D =E6=8B=92=E7=BB=9D=E8=BF=9B=E4=B8=80=E6=AD=A5=E5=AD=98=E5=82=A8=E8=AF=
=A5=E4=BA=A4=E6=8D=A2=E7=B1=BB=E5=9E=8B=E3=80=82
> -
> -=E4=B8=80=E6=97=A6=E4=B8=80=E4=B8=AA=E9=A1=B5=E9=9D=A2=E8=A2=AB=E6=88=90=
=E5=8A=9F=E5=AD=98=E5=82=A8=EF=BC=8C=E5=9C=A8=E8=AF=A5=E9=A1=B5=E9=9D=A2=E4=
=B8=8A=E7=9A=84=E5=8C=B9=E9=85=8D=E5=8A=A0=E8=BD=BD=E9=80=9A=E5=B8=B8=E4=BC=
=9A=E6=88=90=E5=8A=9F=E3=80=82=E5=9B=A0=E6=AD=A4=EF=BC=8C=E5=BD=93=E5=86=85=
=E6=A0=B8=E5=8F=91=E7=8E=B0=E8=87=AA=E5=B7=B1=E5=A4=84=E4=BA=8E=E9=9C=80
> -=E8=A6=81=E4=BA=A4=E6=8D=A2=E9=A1=B5=E9=9D=A2=E7=9A=84=E6=83=85=E5=86=B5=
=E6=97=B6=EF=BC=8C=E5=AE=83=E9=A6=96=E5=85=88=E5=B0=9D=E8=AF=95=E4=BD=BF=E7=
=94=A8frontswap=E3=80=82=E5=A6=82=E6=9E=9C=E5=AD=98=E5=82=A8=E7=9A=84=E7=BB=
=93=E6=9E=9C=E6=98=AF=E6=88=90=E5=8A=9F=E7=9A=84=EF=BC=8C=E9=82=A3=E4=B9=88=
=E6=95=B0=E6=8D=AE=E5=B0=B1=E5=B7=B2
> -=E7=BB=8F=E6=88=90=E5=8A=9F=E7=9A=84=E4=BF=9D=E5=AD=98=E5=88=B0=E4=BA=86=
transcendent memory=E4=B8=AD=EF=BC=8C=E5=B9=B6=E4=B8=94=E9=81=BF=E5=85=8D=
=E4=BA=86=E7=A3=81=E7=9B=98=E5=86=99=E5=85=A5=EF=BC=8C=E5=A6=82=E6=9E=9C=E5=
=90=8E=E6=9D=A5=E5=86=8D=E8=AF=BB=E5=9B=9E=E6=95=B0=E6=8D=AE=EF=BC=8C
> -=E4=B9=9F=E9=81=BF=E5=85=8D=E4=BA=86=E7=A3=81=E7=9B=98=E8=AF=BB=E5=8F=96=
=E3=80=82=E5=A6=82=E6=9E=9C=E5=AD=98=E5=82=A8=E8=BF=94=E5=9B=9E=E5=A4=B1=E8=
=B4=A5=EF=BC=8Ctranscendent memory=E5=B7=B2=E7=BB=8F=E6=8B=92=E7=BB=9D=E4=
=BA=86=E8=AF=A5=E6=95=B0=E6=8D=AE=EF=BC=8C=E4=B8=94=E8=AF=A5=E9=A1=B5
> -=E5=8F=AF=E4=BB=A5=E5=83=8F=E5=BE=80=E5=B8=B8=E4=B8=80=E6=A0=B7=E8=A2=AB=
=E5=86=99=E5=85=A5=E4=BA=A4=E6=8D=A2=E7=A9=BA=E9=97=B4=E3=80=82
> -
> -=E8=AF=B7=E6=B3=A8=E6=84=8F=EF=BC=8C=E5=A6=82=E6=9E=9C=E4=B8=80=E4=B8=AA=
=E9=A1=B5=E9=9D=A2=E8=A2=AB=E5=AD=98=E5=82=A8=EF=BC=8C=E8=80=8C=E8=AF=A5=E9=
=A1=B5=E9=9D=A2=E5=B7=B2=E7=BB=8F=E5=AD=98=E5=9C=A8=E4=BA=8Etranscendent me=
mory=E4=B8=AD=EF=BC=88=E4=B8=80=E4=B8=AA =E2=80=9C=E9=87=8D=E5=A4=8D=E2=80=
=9D
> -=E7=9A=84=E5=AD=98=E5=82=A8=EF=BC=89=EF=BC=8C=E8=A6=81=E4=B9=88=E5=AD=98=
=E5=82=A8=E6=88=90=E5=8A=9F=EF=BC=8C=E6=95=B0=E6=8D=AE=E8=A2=AB=E8=A6=86=E7=
=9B=96=EF=BC=8C=E8=A6=81=E4=B9=88=E5=AD=98=E5=82=A8=E5=A4=B1=E8=B4=A5=EF=BC=
=8C=E8=AF=A5=E9=A1=B5=E9=9D=A2=E8=A2=AB=E5=BA=9F=E6=AD=A2=E3=80=82=E8=BF=99=
=E7=A1=AE=E4=BF=9D=E4=BA=86=E6=97=A7=E7=9A=84=E6=95=B0=E6=8D=AE=E6=B0=B8=E8=
=BF=9C
> -=E4=B8=8D=E4=BC=9A=E4=BB=8Efrontswap=E4=B8=AD=E8=8E=B7=E5=BE=97=E3=80=82
> -
> -=E5=A6=82=E6=9E=9C=E9=85=8D=E7=BD=AE=E6=AD=A3=E7=A1=AE=EF=BC=8C=E5=AF=B9=
frontswap=E7=9A=84=E7=9B=91=E6=8E=A7=E6=98=AF=E9=80=9A=E8=BF=87 `/sys/kerne=
l/debug/frontswap` =E7=9B=AE=E5=BD=95=E4=B8=8B=E7=9A=84
> -debugfs=E5=AE=8C=E6=88=90=E7=9A=84=E3=80=82frontswap=E7=9A=84=E6=9C=89=
=E6=95=88=E6=80=A7=E5=8F=AF=E4=BB=A5=E9=80=9A=E8=BF=87=E4=BB=A5=E4=B8=8B=E6=
=96=B9=E5=BC=8F=E6=B5=8B=E9=87=8F=EF=BC=88=E5=9C=A8=E6=89=80=E6=9C=89=E4=BA=
=A4=E6=8D=A2=E8=AE=BE=E5=A4=87=E4=B8=AD=EF=BC=89:
> -
> -``failed_stores``
> -       =E6=9C=89=E5=A4=9A=E5=B0=91=E6=AC=A1=E5=AD=98=E5=82=A8=E7=9A=84=
=E5=B0=9D=E8=AF=95=E6=98=AF=E5=A4=B1=E8=B4=A5=E7=9A=84
> -
> -``loads``
> -       =E5=B0=9D=E8=AF=95=E4=BA=86=E5=A4=9A=E5=B0=91=E6=AC=A1=E5=8A=A0=
=E8=BD=BD=EF=BC=88=E5=BA=94=E8=AF=A5=E5=85=A8=E9=83=A8=E6=88=90=E5=8A=9F=EF=
=BC=89
> -
> -``succ_stores``
> -       =E6=9C=89=E5=A4=9A=E5=B0=91=E6=AC=A1=E5=AD=98=E5=82=A8=E7=9A=84=
=E5=B0=9D=E8=AF=95=E6=98=AF=E6=88=90=E5=8A=9F=E7=9A=84
> -
> -``invalidates``
> -       =E5=B0=9D=E8=AF=95=E4=BA=86=E5=A4=9A=E5=B0=91=E6=AC=A1=E4=BD=9C=
=E5=BA=9F
> -
> -=E5=90=8E=E5=8F=B0=E5=AE=9E=E7=8E=B0=E5=8F=AF=E4=BB=A5=E6=8F=90=E4=BE=9B=
=E9=A2=9D=E5=A4=96=E7=9A=84=E6=8C=87=E6=A0=87=E3=80=82
> -
> -=E7=BB=8F=E5=B8=B8=E9=97=AE=E5=88=B0=E7=9A=84=E9=97=AE=E9=A2=98
> -=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> -
> -* =E4=BB=B7=E5=80=BC=E5=9C=A8=E5=93=AA=E9=87=8C?
> -
> -=E5=BD=93=E4=B8=80=E4=B8=AA=E5=B7=A5=E4=BD=9C=E8=B4=9F=E8=BD=BD=E5=BC=80=
=E5=A7=8B=E4=BA=A4=E6=8D=A2=E6=97=B6=EF=BC=8C=E6=80=A7=E8=83=BD=E5=B0=B1=E4=
=BC=9A=E4=B8=8B=E9=99=8D=E3=80=82Frontswap=E9=80=9A=E8=BF=87=E6=8F=90=E4=BE=
=9B=E4=B8=80=E4=B8=AA=E5=B9=B2=E5=87=80=E7=9A=84=E3=80=81=E5=8A=A8=E6=80=81=
=E7=9A=84=E6=8E=A5=E5=8F=A3=E6=9D=A5
> -=E8=AF=BB=E5=8F=96=E5=92=8C=E5=86=99=E5=85=A5=E4=BA=A4=E6=8D=A2=E9=A1=B5=
=E5=88=B0 =E2=80=9Ctranscendent memory=E2=80=9D=EF=BC=8C=E4=BB=8E=E8=80=8C=
=E5=A4=A7=E5=A4=A7=E5=A2=9E=E5=8A=A0=E4=BA=86=E8=AE=B8=E5=A4=9A=E8=BF=99=E6=
=A0=B7=E7=9A=84=E5=B7=A5=E4=BD=9C=E8=B4=9F=E8=BD=BD=E7=9A=84=E6=80=A7
> -=E8=83=BD=EF=BC=8C=E5=90=A6=E5=88=99=E5=86=85=E6=A0=B8=E6=98=AF=E6=97=A0=
=E6=B3=95=E7=9B=B4=E6=8E=A5=E5=AF=BB=E5=9D=80=E7=9A=84=E3=80=82=E5=BD=93=E6=
=95=B0=E6=8D=AE=E8=A2=AB=E8=BD=AC=E6=8D=A2=E4=B8=BA=E4=B8=8D=E5=90=8C=E7=9A=
=84=E5=BD=A2=E5=BC=8F=E5=92=8C=E5=A4=A7=E5=B0=8F=EF=BC=88=E6=AF=94=E5=A6=82=
=E5=8E=8B=E7=BC=A9=EF=BC=89=E6=88=96=E8=80=85=E8=A2=AB=E7=A7=98=E5=AF=86
> -=E7=A7=BB=E5=8A=A8=EF=BC=88=E5=AF=B9=E4=BA=8E=E4=B8=80=E4=BA=9B=E7=B1=BB=
=E4=BC=BCRAM=E7=9A=84=E8=AE=BE=E5=A4=87=E6=9D=A5=E8=AF=B4=EF=BC=8C=E8=BF=99=
=E5=8F=AF=E8=83=BD=E5=AF=B9=E5=86=99=E5=B9=B3=E8=A1=A1=E5=BE=88=E6=9C=89=E7=
=94=A8=EF=BC=89=E6=97=B6=EF=BC=8C=E8=BF=99=E4=B8=AA=E6=8E=A5=E5=8F=A3=E6=98=
=AF=E7=90=86=E6=83=B3=E7=9A=84=E3=80=82=E4=BA=A4=E6=8D=A2
> -=E9=A1=B5=EF=BC=88=E5=92=8C=E8=A2=AB=E9=A9=B1=E9=80=90=E7=9A=84=E9=A1=B5=
=E9=9D=A2=E7=BC=93=E5=AD=98=E9=A1=B5=EF=BC=89=E6=98=AF=E8=BF=99=E7=A7=8D=E6=
=AF=94RAM=E6=85=A2=E4=BD=86=E6=AF=94=E7=A3=81=E7=9B=98=E5=BF=AB=E5=BE=97=E5=
=A4=9A=E7=9A=84=E2=80=9C=E4=BC=AARAM=E8=AE=BE=E5=A4=87=E2=80=9D=E7=9A=84=E4=
=B8=80=E5=A4=A7=E7=94=A8=E9=80=94=E3=80=82
> -
> -Frontswap=E5=AF=B9=E5=86=85=E6=A0=B8=E7=9A=84=E5=BD=B1=E5=93=8D=E7=9B=B8=
=E5=BD=93=E5=B0=8F=EF=BC=8C=E4=B8=BA=E5=90=84=E7=A7=8D=E7=B3=BB=E7=BB=9F=E9=
=85=8D=E7=BD=AE=E4=B8=AD=E6=9B=B4=E5=8A=A8=E6=80=81=E3=80=81=E6=9B=B4=E7=81=
=B5=E6=B4=BB=E7=9A=84RAM=E5=88=A9=E7=94=A8=E6=8F=90=E4=BE=9B=E4=BA=86=E5=B7=
=A8=E5=A4=A7=E7=9A=84
> -=E7=81=B5=E6=B4=BB=E6=80=A7=EF=BC=9A
> -
> -=E5=9C=A8=E5=8D=95=E4=B8=80=E5=86=85=E6=A0=B8=E7=9A=84=E6=83=85=E5=86=B5=
=E4=B8=8B=EF=BC=8C=E5=8F=88=E7=A7=B0=E2=80=9Czcache=E2=80=9D=EF=BC=8C=E9=A1=
=B5=E9=9D=A2=E8=A2=AB=E5=8E=8B=E7=BC=A9=E5=B9=B6=E5=AD=98=E5=82=A8=E5=9C=A8=
=E6=9C=AC=E5=9C=B0=E5=86=85=E5=AD=98=E4=B8=AD=EF=BC=8C=E4=BB=8E=E8=80=8C=E5=
=A2=9E=E5=8A=A0=E4=BA=86=E5=8F=AF=E4=BB=A5=E5=AE=89
> -=E5=85=A8=E4=BF=9D=E5=AD=98=E5=9C=A8RAM=E4=B8=AD=E7=9A=84=E5=8C=BF=E5=90=
=8D=E9=A1=B5=E9=9D=A2=E6=80=BB=E6=95=B0=E3=80=82Zcache=E6=9C=AC=E8=B4=A8=E4=
=B8=8A=E6=98=AF=E7=94=A8=E5=8E=8B=E7=BC=A9/=E8=A7=A3=E5=8E=8B=E7=BC=A9=E7=
=9A=84CPU=E5=91=A8=E6=9C=9F=E6=8D=A2=E5=8F=96=E6=9B=B4=E5=A5=BD=E7=9A=84=E5=
=86=85=E5=AD=98=E5=88=A9
> -=E7=94=A8=E7=8E=87=E3=80=82Benchmarks=E6=B5=8B=E8=AF=95=E6=98=BE=E7=A4=
=BA=EF=BC=8C=E5=BD=93=E5=86=85=E5=AD=98=E5=8E=8B=E5=8A=9B=E8=BE=83=E4=BD=8E=
=E6=97=B6=EF=BC=8C=E5=87=A0=E4=B9=8E=E6=B2=A1=E6=9C=89=E5=BD=B1=E5=93=8D=EF=
=BC=8C=E8=80=8C=E5=9C=A8=E9=AB=98=E5=86=85=E5=AD=98=E5=8E=8B=E5=8A=9B=E4=B8=
=8B=E7=9A=84=E4=B8=80=E4=BA=9B
> -=E5=B7=A5=E4=BD=9C=E8=B4=9F=E8=BD=BD=E4=B8=8A=EF=BC=8C=E5=88=99=E6=9C=89=
=E6=98=8E=E6=98=BE=E7=9A=84=E6=80=A7=E8=83=BD=E6=94=B9=E5=96=84=EF=BC=8825%=
=E4=BB=A5=E4=B8=8A=EF=BC=89=E3=80=82
> -
> -=E2=80=9CRAMster=E2=80=9D =E5=9C=A8zcache=E7=9A=84=E5=9F=BA=E7=A1=80=E4=
=B8=8A=E5=A2=9E=E5=8A=A0=E4=BA=86=E5=AF=B9=E9=9B=86=E7=BE=A4=E7=B3=BB=E7=BB=
=9F=E7=9A=84 =E2=80=9Cpeer-to-peer=E2=80=9D transcendent memory
> -=E7=9A=84=E6=94=AF=E6=8C=81=E3=80=82Frontswap=E9=A1=B5=E9=9D=A2=E5=83=8F=
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> -=E7=BB=9F=E7=9A=84RAM=E3=80=82=E8=BF=99=E4=BD=BF=E5=BE=97RAM=E5=8F=AF=E4=
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> -=E4=BA=A4=E6=8D=A2=E5=88=B0=E7=B3=BB=E7=BB=9FB=EF=BC=8C=E5=8F=8D=E4=B9=
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> -=E5=8F=AF=E4=BB=A5=E6=A0=B9=E6=8D=AE=E9=9C=80=E8=A6=81=E5=8A=A8=E6=80=81=
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> -=E6=9C=89=E5=A4=9A=E5=B0=91=E5=86=85=E5=AD=98=E5=8F=AF=E7=94=A8
> -
> -=E5=9C=A8=E8=99=9A=E6=8B=9F=E6=83=85=E5=86=B5=E4=B8=8B=EF=BC=8C=E8=99=9A=
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> -=E7=94=A8=E3=80=82=E5=AF=B9=E4=BA=8ERAM=E6=9D=A5=E8=AF=B4=EF=BC=8C=E8=BF=
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> -=E6=98=AF=E5=A4=B1=E8=B4=A5=E7=9A=84=EF=BC=88=E9=99=A4=E4=BA=86=E4=B8=80=
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> -=E5=90=8E=E7=AB=AF=E5=85=81=E8=AE=B8=E7=AE=A1=E7=90=86=E5=99=A8=E6=8B=A5=
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> -=E8=80=8C=E4=B8=94=E9=A1=B5=E9=9D=A2=E5=8F=AF=E4=BB=A5=E8=A2=AB=E5=8E=8B=
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> -=E7=9A=84RAM=E6=97=B6=EF=BC=88=E5=A6=82 =E2=80=9Cselfballooning=E2=80=9D=
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> -=E5=85=81=E8=AE=B8=E8=BF=99=E4=BA=9B=E9=A1=B5=E9=9D=A2=E8=A2=AB=E4=BA=A4=
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> -=E4=BB=8E=E8=80=8C=E5=87=8F=E8=BD=BB=E8=AE=A1=E5=88=92=E5=A4=96=E4=BA=A4=
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> -
> -=E4=B8=80=E4=B8=AAKVM=E7=9A=84=E5=AE=9E=E7=8E=B0=E6=AD=A3=E5=9C=A8=E8=BF=
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> -=E5=86=85=E5=AD=98=E6=89=A9=E5=B1=95=E6=8A=80=E6=9C=AF=E7=9A=84=E8=B0=83=
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> -
> -* =E5=BD=93=E7=84=B6=EF=BC=8C=E5=9C=A8=E6=9F=90=E4=BA=9B=E6=83=85=E5=86=
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> -
> -=E5=A6=82=E6=9E=9C CONFIG_FRONTSWAP =E8=A2=AB=E7=A6=81=E7=94=A8=EF=BC=8C=
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> -=E4=B8=AA swapon'ed swap =E8=AE=BE=E5=A4=87=E7=9A=84=E5=87=A0=E4=B8=AA=
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> -frontswap=E7=9A=84 =E2=80=9Cbackend=E2=80=9D =E5=AF=84=E5=AD=98=E5=99=A8=
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> -=E6=98=AF=E9=9B=B6=E3=80=82=E5=A6=82=E6=9E=9C CONFIG_FRONTSWAP =E8=A2=AB=
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> -=E5=90=8E=E7=AB=AF=E6=AF=8F=E6=AC=A1 =E2=80=9Cstore=E2=80=9D =E8=AF=B7=
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> -=E5=BF=BD=E7=95=A5=E4=B8=8D=E8=AE=A1 - =E5=9B=A0=E4=B8=BA=E6=AF=8F=E6=AC=
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> -=E7=9A=84=EF=BC=8C=E6=97=A0=E8=AE=BA=E5=A6=82=E4=BD=95=E4=BD=BF=E7=94=A8=
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> -
> -=E8=87=B3=E4=BA=8E=E7=A9=BA=E9=97=B4=EF=BC=8C=E5=A6=82=E6=9E=9CCONFIG_FR=
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> -=E6=AF=8F=E4=B8=AA=E4=BA=A4=E6=8D=A2=E8=AE=BE=E5=A4=87=E7=9A=84=E6=AF=8F=
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> -=E9=A1=B5=E5=88=86=E9=85=8D=E7=9A=848=E4=BD=8D=EF=BC=88=E5=9C=A82.6.34=
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> -=E4=BC=9A=E5=81=B7=E5=8F=96=E7=8E=B0=E6=9C=89=E7=9A=848=E4=B8=AA=E6=AF=
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> -=E9=9D=9E=E5=B8=B8=E5=A4=A7=E7=9A=84=E4=BA=A4=E6=8D=A2=E7=9B=98=EF=BC=88=
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> -
> -=E5=BD=93=E4=BA=A4=E6=8D=A2=E9=A1=B5=E5=AD=98=E5=82=A8=E5=9C=A8transcend=
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> -=E4=BA=A7=E7=94=9F=E6=9B=B4=E5=A4=9A=E7=9A=84=E5=86=85=E5=AD=98=E5=8E=8B=
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> -=E6=9D=A5=E4=BB=94=E7=BB=86=EF=BC=88=E4=BD=86=E5=8A=A8=E6=80=81=E5=9C=B0=
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> -
> -* =E5=A5=BD=E5=90=A7=EF=BC=8C=E9=82=A3=E5=B0=B1=E7=94=A8=E5=86=85=E6=A0=
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> -
> -=E6=88=91=E4=BB=AC=E5=81=87=E8=AE=BE=E5=9C=A8=E5=86=85=E6=A0=B8=E5=88=9D=
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> -=E6=AF=8F=E5=BD=93=E4=B8=80=E4=B8=AA=E4=BA=A4=E6=8D=A2=E8=AE=BE=E5=A4=87=
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> -=E6=8D=A2=E9=A1=B5=E7=9A=84=E5=B0=9D=E8=AF=95=E3=80=82
> -
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> -=E4=B8=8B=EF=BC=8Cfrontswap=E5=9C=A8=E4=BA=A4=E6=8D=A2=E8=AE=BE=E5=A4=87=
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> -=E9=A1=B5=E9=9D=A2=E5=81=8F=E7=A7=BB=E9=87=8F=EF=BC=8C=E5=90=A6=E5=88=99=
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> -
> -=E5=BD=93=E4=BA=A4=E6=8D=A2=E5=AD=90=E7=B3=BB=E7=BB=9F=E9=9C=80=E8=A6=81=
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> -=E4=BB=A5=E4=BE=BF=E4=BB=8E=E7=9C=9F=E6=AD=A3=E7=9A=84=E4=BA=A4=E6=8D=A2=
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> -
> -=E6=89=80=E4=BB=A5=E6=AF=8F=E6=AC=A1frontswap backend=E6=8E=A5=E5=8F=97=
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> -=E5=85=A5=E9=83=BD=E8=A2=AB =E2=80=9Cfrontswap backend store=E2=80=9D =
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> -=E6=89=80=E5=8F=96=E4=BB=A3=EF=BC=8C=E8=BF=99=E5=8F=AF=E8=83=BD=E4=BC=9A=
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> -
> -* frontswap=E4=B8=8D=E8=83=BD=E8=A2=AB=E9=85=8D=E7=BD=AE=E4=B8=BA=E4=B8=
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> -  =E8=AE=BE=E5=A4=87=EF=BC=88=E4=BE=8B=E5=A6=82=E5=83=8Fzswap=EF=BC=8C=
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> -
> -=E9=A6=96=E5=85=88=EF=BC=8C=E7=8E=B0=E6=9C=89=E7=9A=84=E4=BA=A4=E6=8D=A2=
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> -
> -=E4=BE=8B=E5=A6=82=EF=BC=8Cfrontswap backend=E5=AF=B9=E4=BB=BB=E4=BD=95=
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> -=E7=9A=84=E5=AE=9A=E4=B9=89=E8=87=B3=E5=85=B3=E9=87=8D=E8=A6=81=EF=BC=8C=
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> -=E5=85=88=E7=9F=A5=E9=81=93=E4=B8=80=E4=B8=AA=E9=A1=B5=E9=9D=A2=E7=9A=84=
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> -
> -=E6=AD=A4=E5=A4=96=EF=BC=8Cfrontswap=E6=98=AF=E5=AE=8C=E5=85=A8=E5=90=8C=
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=B8=8D=E5=BF=85=E8=A6=81=E5=9C=B0=E5=A4=A7=E5=A4=A7=E5=A2=9E=E5=8A=A0fronts=
wap=E5=92=8C/=E6=88=96=E5=9D=97I/O=E5=AD=90=E7=B3=BB=E7=BB=9F=E7=9A=84
> -=E5=A4=8D=E6=9D=82=E6=80=A7=E3=80=82=E4=B9=9F=E5=B0=B1=E6=98=AF=E8=AF=B4=
=EF=BC=8C=E5=8F=AA=E6=9C=89=E6=9C=80=E5=88=9D=E7=9A=84 =E2=80=9Cstore=E2=80=
=9D =E5=92=8C =E2=80=9Cload=E2=80=9D =E6=93=8D=E4=BD=9C=E6=98=AF=E9=9C=80=
=E8=A6=81=E5=90=8C=E6=AD=A5=E7=9A=84=E3=80=82=E4=B8=80=E4=B8=AA=E7=8B=AC=E7=
=AB=8B
> -=E7=9A=84=E5=BC=82=E6=AD=A5=E7=BA=BF=E7=A8=8B=E5=8F=AF=E4=BB=A5=E8=87=AA=
=E7=94=B1=E5=9C=B0=E6=93=8D=E4=BD=9C=E7=94=B1frontswap=E5=AD=98=E5=82=A8=E7=
=9A=84=E9=A1=B5=E9=9D=A2=E3=80=82=E4=BE=8B=E5=A6=82=EF=BC=8CRAMster=E4=B8=
=AD=E7=9A=84 =E2=80=9Cremotification=E2=80=9D
> -=E7=BA=BF=E7=A8=8B=E4=BD=BF=E7=94=A8=E6=A0=87=E5=87=86=E7=9A=84=E5=BC=82=
=E6=AD=A5=E5=86=85=E6=A0=B8=E5=A5=97=E6=8E=A5=E5=AD=97=EF=BC=8C=E5=B0=86=E5=
=8E=8B=E7=BC=A9=E7=9A=84frontswap=E9=A1=B5=E9=9D=A2=E7=A7=BB=E5=8A=A8=E5=88=
=B0=E8=BF=9C=E7=A8=8B=E6=9C=BA=E5=99=A8=E3=80=82=E5=90=8C=E6=A0=B7=EF=BC=8C
> -KVM=E7=9A=84=E5=AE=A2=E6=88=B7=E6=96=B9=E5=AE=9E=E7=8E=B0=E5=8F=AF=E4=BB=
=A5=E8=BF=9B=E8=A1=8C=E5=AE=A2=E6=88=B7=E5=86=85=E5=8E=8B=E7=BC=A9=EF=BC=8C=
=E5=B9=B6=E4=BD=BF=E7=94=A8 =E2=80=9Cbatched=E2=80=9D hypercalls=E3=80=82
> -
> -=E5=9C=A8=E8=99=9A=E6=8B=9F=E5=8C=96=E7=8E=AF=E5=A2=83=E4=B8=AD=EF=BC=8C=
=E5=8A=A8=E6=80=81=E6=80=A7=E5=85=81=E8=AE=B8=E7=AE=A1=E7=90=86=E7=A8=8B=E5=
=BA=8F=EF=BC=88=E6=88=96=E4=B8=BB=E6=9C=BA=E6=93=8D=E4=BD=9C=E7=B3=BB=E7=BB=
=9F=EF=BC=89=E5=81=9A=E2=80=9Cintelligent overcommit=E2=80=9D=E3=80=82
> -=E4=BE=8B=E5=A6=82=EF=BC=8C=E5=AE=83=E5=8F=AF=E4=BB=A5=E9=80=89=E6=8B=A9=
=E5=8F=AA=E6=8E=A5=E5=8F=97=E9=A1=B5=E9=9D=A2=EF=BC=8C=E7=9B=B4=E5=88=B0=E4=
=B8=BB=E6=9C=BA=E4=BA=A4=E6=8D=A2=E5=8F=AF=E8=83=BD=E5=8D=B3=E5=B0=86=E5=8F=
=91=E7=94=9F=EF=BC=8C=E7=84=B6=E5=90=8E=E5=BC=BA=E8=BF=AB=E5=AE=A2=E6=88=B7=
=E6=9C=BA=E5=81=9A=E4=BB=96=E4=BB=AC
> -=E8=87=AA=E5=B7=B1=E7=9A=84=E4=BA=A4=E6=8D=A2=E3=80=82
> -
> -transcendent memory=E8=A7=84=E6=A0=BC=E7=9A=84frontswap=E6=9C=89=E4=B8=
=80=E4=B8=AA=E5=9D=8F=E5=A4=84=E3=80=82=E5=9B=A0=E4=B8=BA=E4=BB=BB=E4=BD=95=
 =E2=80=9Cstore=E2=80=9D =E9=83=BD=E5=8F=AF
> -=E8=83=BD=E5=A4=B1=E8=B4=A5=EF=BC=8C=E6=89=80=E4=BB=A5=E5=BF=85=E9=A1=BB=
=E5=9C=A8=E4=B8=80=E4=B8=AA=E7=9C=9F=E6=AD=A3=E7=9A=84=E4=BA=A4=E6=8D=A2=E8=
=AE=BE=E5=A4=87=E4=B8=8A=E6=9C=89=E4=B8=80=E4=B8=AA=E7=9C=9F=E6=AD=A3=E7=9A=
=84=E6=8F=92=E6=A7=BD=E6=9D=A5=E4=BA=A4=E6=8D=A2=E9=A1=B5=E9=9D=A2=E3=80=82=
=E5=9B=A0=E6=AD=A4=EF=BC=8C
> -frontswap=E5=BF=85=E9=A1=BB=E4=BD=9C=E4=B8=BA=E6=AF=8F=E4=B8=AA=E4=BA=A4=
=E6=8D=A2=E8=AE=BE=E5=A4=87=E7=9A=84 =E2=80=9C=E5=BD=B1=E5=AD=90=E2=80=9D =
=E6=9D=A5=E5=AE=9E=E7=8E=B0=EF=BC=8C=E5=AE=83=E6=9C=89=E5=8F=AF=E8=83=BD=E5=
=AE=B9=E7=BA=B3=E4=BA=A4=E6=8D=A2=E8=AE=BE=E5=A4=87=E5=8F=AF=E8=83=BD
> -=E5=AE=B9=E7=BA=B3=E7=9A=84=E6=AF=8F=E4=B8=80=E4=B8=AA=E9=A1=B5=E9=9D=A2=
=EF=BC=8C=E4=B9=9F=E6=9C=89=E5=8F=AF=E8=83=BD=E6=A0=B9=E6=9C=AC=E4=B8=8D=E5=
=AE=B9=E7=BA=B3=E4=BB=BB=E4=BD=95=E9=A1=B5=E9=9D=A2=E3=80=82=E8=BF=99=E6=84=
=8F=E5=91=B3=E7=9D=80frontswap=E4=B8=8D=E8=83=BD=E5=8C=85=E5=90=AB=E6=AF=94
> -swap=E8=AE=BE=E5=A4=87=E6=80=BB=E6=95=B0=E6=9B=B4=E5=A4=9A=E7=9A=84=E9=
=A1=B5=E9=9D=A2=E3=80=82=E4=BE=8B=E5=A6=82=EF=BC=8C=E5=A6=82=E6=9E=9C=E5=9C=
=A8=E6=9F=90=E4=BA=9B=E5=AE=89=E8=A3=85=E4=B8=8A=E6=B2=A1=E6=9C=89=E9=85=8D=
=E7=BD=AE=E4=BA=A4=E6=8D=A2=E8=AE=BE=E5=A4=87=EF=BC=8Cfrontswap
> -=E5=B0=B1=E6=B2=A1=E6=9C=89=E7=94=A8=E3=80=82=E6=97=A0=E4=BA=A4=E6=8D=A2=
=E8=AE=BE=E5=A4=87=E7=9A=84=E4=BE=BF=E6=90=BA=E5=BC=8F=E8=AE=BE=E5=A4=87=E4=
=BB=8D=E7=84=B6=E5=8F=AF=E4=BB=A5=E4=BD=BF=E7=94=A8frontswap=EF=BC=8C=E4=BD=
=86=E6=98=AF=E8=BF=99=E7=A7=8D=E8=AE=BE=E5=A4=87=E7=9A=84
> -backend=E5=BF=85=E9=A1=BB=E9=85=8D=E7=BD=AE=E6=9F=90=E7=A7=8D =E2=80=9Cg=
host=E2=80=9D =E4=BA=A4=E6=8D=A2=E8=AE=BE=E5=A4=87=EF=BC=8C=E5=B9=B6=E7=A1=
=AE=E4=BF=9D=E5=AE=83=E6=B0=B8=E8=BF=9C=E4=B8=8D=E4=BC=9A=E8=A2=AB=E4=BD=BF=
=E7=94=A8=E3=80=82
> -
> -
> -* =E4=B8=BA=E4=BB=80=E4=B9=88=E4=BC=9A=E6=9C=89=E8=BF=99=E7=A7=8D=E5=85=
=B3=E4=BA=8E =E2=80=9C=E9=87=8D=E5=A4=8D=E5=AD=98=E5=82=A8=E2=80=9D =E7=9A=
=84=E5=A5=87=E6=80=AA=E5=AE=9A=E4=B9=89=EF=BC=9F=E5=A6=82=E6=9E=9C=E4=B8=80=
=E4=B8=AA=E9=A1=B5=E9=9D=A2=E4=BB=A5=E5=89=8D=E8=A2=AB=E6=88=90=E5=8A=9F=E5=
=9C=B0=E5=AD=98=E5=82=A8=E8=BF=87=EF=BC=8C
> -  =E9=9A=BE=E9=81=93=E5=AE=83=E4=B8=8D=E8=83=BD=E6=80=BB=E6=98=AF=E8=A2=
=AB=E6=88=90=E5=8A=9F=E5=9C=B0=E8=A6=86=E7=9B=96=E5=90=97=EF=BC=9F
> -
> -=E5=87=A0=E4=B9=8E=E6=80=BB=E6=98=AF=E5=8F=AF=E4=BB=A5=E7=9A=84=EF=BC=8C=
=E4=B8=8D=EF=BC=8C=E6=9C=89=E6=97=B6=E4=B8=8D=E8=83=BD=E3=80=82=E8=80=83=E8=
=99=91=E4=B8=80=E4=B8=AA=E4=BE=8B=E5=AD=90=EF=BC=8C=E6=95=B0=E6=8D=AE=E8=A2=
=AB=E5=8E=8B=E7=BC=A9=E4=BA=86=EF=BC=8C=E5=8E=9F=E6=9D=A5=E7=9A=844K=E9=A1=
=B5=E9=9D=A2=E8=A2=AB=E5=8E=8B
> -=E7=BC=A9=E5=88=B0=E4=BA=861K=E3=80=82=E7=8E=B0=E5=9C=A8=EF=BC=8C=E6=9C=
=89=E4=BA=BA=E8=AF=95=E5=9B=BE=E7=94=A8=E4=B8=8D=E5=8F=AF=E5=8E=8B=E7=BC=A9=
=E7=9A=84=E6=95=B0=E6=8D=AE=E8=A6=86=E7=9B=96=E8=AF=A5=E9=A1=B5=EF=BC=8C=E5=
=9B=A0=E6=AD=A4=E4=BC=9A=E5=8D=A0=E7=94=A8=E6=95=B4=E4=B8=AA4K=E3=80=82=E4=
=BD=86=E6=98=AF
> -backend=E6=B2=A1=E6=9C=89=E6=9B=B4=E5=A4=9A=E7=9A=84=E7=A9=BA=E9=97=B4=
=E4=BA=86=E3=80=82=E5=9C=A8=E8=BF=99=E7=A7=8D=E6=83=85=E5=86=B5=E4=B8=8B=EF=
=BC=8C=E8=BF=99=E4=B8=AA=E5=AD=98=E5=82=A8=E5=BF=85=E9=A1=BB=E8=A2=AB=E6=8B=
=92=E7=BB=9D=E3=80=82=E6=AF=8F=E5=BD=93frontswap
> -=E6=8B=92=E7=BB=9D=E4=B8=80=E4=B8=AA=E4=BC=9A=E8=A6=86=E7=9B=96=E7=9A=84=
=E5=AD=98=E5=82=A8=E6=97=B6=EF=BC=8C=E5=AE=83=E4=B9=9F=E5=BF=85=E9=A1=BB=E4=
=BD=BF=E6=97=A7=E7=9A=84=E6=95=B0=E6=8D=AE=E4=BD=9C=E5=BA=9F=EF=BC=8C=E5=B9=
=B6=E7=A1=AE=E4=BF=9D=E5=AE=83=E4=B8=8D=E5=86=8D=E8=A2=AB=E8=AE=BF=E9=97=AE=
=E3=80=82=E5=9B=A0=E4=B8=BA=E4=BA=A4
> -=E6=8D=A2=E5=AD=90=E7=B3=BB=E7=BB=9F=E4=BC=9A=E6=8A=8A=E6=96=B0=E7=9A=84=
=E6=95=B0=E6=8D=AE=E5=86=99=E5=88=B0=E8=AF=BB=E4=BA=A4=E6=8D=A2=E8=AE=BE=E5=
=A4=87=E4=B8=8A=EF=BC=8C=E8=BF=99=E6=98=AF=E7=A1=AE=E4=BF=9D=E4=B8=80=E8=87=
=B4=E6=80=A7=E7=9A=84=E6=AD=A3=E7=A1=AE=E5=81=9A=E6=B3=95=E3=80=82
> -
> -* =E4=B8=BA=E4=BB=80=E4=B9=88frontswap=E8=A1=A5=E4=B8=81=E4=BC=9A=E5=88=
=9B=E5=BB=BA=E6=96=B0=E7=9A=84=E5=A4=B4=E6=96=87=E4=BB=B6swapfile.h=EF=BC=
=9F
> -
> -frontswap=E4=BB=A3=E7=A0=81=E4=BE=9D=E8=B5=96=E4=BA=8E=E4=B8=80=E4=BA=9B=
swap=E5=AD=90=E7=B3=BB=E7=BB=9F=E5=86=85=E9=83=A8=E7=9A=84=E6=95=B0=E6=8D=
=AE=E7=BB=93=E6=9E=84=EF=BC=8C=E8=BF=99=E4=BA=9B=E6=95=B0=E6=8D=AE=E7=BB=93=
=E6=9E=84=E5=A4=9A=E5=B9=B4=E6=9D=A5=E4=B8=80=E7=9B=B4
> -=E5=9C=A8=E9=9D=99=E6=80=81=E5=92=8C=E5=85=A8=E5=B1=80=E4=B9=8B=E9=97=B4=
=E6=9D=A5=E5=9B=9E=E7=A7=BB=E5=8A=A8=E3=80=82=E8=BF=99=E4=BC=BC=E4=B9=8E=E6=
=98=AF=E4=B8=80=E4=B8=AA=E5=90=88=E7=90=86=E7=9A=84=E5=A6=A5=E5=8D=8F=EF=BC=
=9A=E5=B0=86=E5=AE=83=E4=BB=AC=E5=AE=9A=E4=B9=89=E4=B8=BA=E5=85=A8=E5=B1=80=
=EF=BC=8C=E4=BD=86=E5=9C=A8=E4=B8=80
> -=E4=B8=AA=E6=96=B0=E7=9A=84=E5=8C=85=E5=90=AB=E6=96=87=E4=BB=B6=E4=B8=AD=
=E5=A3=B0=E6=98=8E=E5=AE=83=E4=BB=AC=EF=BC=8C=E8=AF=A5=E6=96=87=E4=BB=B6=E4=
=B8=8D=E8=A2=AB=E5=8C=85=E5=90=ABswap.h=E7=9A=84=E5=A4=A7=E9=87=8F=E6=BA=90=
=E6=96=87=E4=BB=B6=E6=89=80=E5=8C=85=E5=90=AB=E3=80=82
> -
> -Dan Magenheimer=EF=BC=8C=E6=9C=80=E5=90=8E=E6=9B=B4=E6=96=B0=E4=BA=8E201=
2=E5=B9=B44=E6=9C=889=E6=97=A5
> diff --git a/Documentation/translations/zh_CN/mm/index.rst b/Documentatio=
n/translations/zh_CN/mm/index.rst
> index 2f53e37b8049..b950dd118be7 100644
> --- a/Documentation/translations/zh_CN/mm/index.rst
> +++ b/Documentation/translations/zh_CN/mm/index.rst
> @@ -42,7 +42,6 @@ =E7=BB=93=E6=9E=84=E5=8C=96=E7=9A=84=E6=96=87=E6=A1=A3=
=E4=B8=AD=EF=BC=8C=E5=A6=82=E6=9E=9C=E5=AE=83=E5=B7=B2=E7=BB=8F=E5=AE=8C=E6=
=88=90=E4=BA=86=E5=AE=83=E7=9A=84=E4=BD=BF=E5=91=BD=EF=BC=8C=E5=8F=AF=E4=BB=
=A5=E5=88=A0=E9=99=A4=E3=80=82
>     damon/index
>     free_page_reporting
>     ksm
> -   frontswap
>     hmm
>     hwpoison
>     hugetlbfs_reserv
> diff --git a/MAINTAINERS b/MAINTAINERS
> index dfbb271f1667..f2bb2f9eaccf 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -8394,13 +8394,6 @@ F:       Documentation/power/freezing-of-tasks.rst
>  F:     include/linux/freezer.h
>  F:     kernel/freezer.c
>
> -FRONTSWAP API
> -M:     Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> -L:     linux-kernel@vger.kernel.org
> -S:     Maintained
> -F:     include/linux/frontswap.h
> -F:     mm/frontswap.c
> -
>  FS-CACHE: LOCAL CACHING FOR NETWORK FILESYSTEMS
>  M:     David Howells <dhowells@redhat.com>
>  L:     linux-cachefs@redhat.com (moderated for non-subscribers)
> diff --git a/fs/proc/meminfo.c b/fs/proc/meminfo.c
> index 8dca4d6d96c7..74e3c3815696 100644
> --- a/fs/proc/meminfo.c
> +++ b/fs/proc/meminfo.c
> @@ -17,6 +17,7 @@
>  #ifdef CONFIG_CMA
>  #include <linux/cma.h>
>  #endif
> +#include <linux/zswap.h>
>  #include <asm/page.h>
>  #include "internal.h"
>
> diff --git a/include/linux/frontswap.h b/include/linux/frontswap.h
> deleted file mode 100644
> index eaa0ac5f9003..000000000000
> --- a/include/linux/frontswap.h
> +++ /dev/null
> @@ -1,91 +0,0 @@
> -/* SPDX-License-Identifier: GPL-2.0 */
> -#ifndef _LINUX_FRONTSWAP_H
> -#define _LINUX_FRONTSWAP_H
> -
> -#include <linux/swap.h>
> -#include <linux/mm.h>
> -#include <linux/bitops.h>
> -#include <linux/jump_label.h>
> -
> -struct frontswap_ops {
> -       void (*init)(unsigned); /* this swap type was just swapon'ed */
> -       int (*store)(unsigned, pgoff_t, struct page *); /* store a page *=
/
> -       int (*load)(unsigned, pgoff_t, struct page *, bool *); /* load a =
page */
> -       void (*invalidate_page)(unsigned, pgoff_t); /* page no longer nee=
ded */
> -       void (*invalidate_area)(unsigned); /* swap type just swapoff'ed *=
/
> -};
> -
> -int frontswap_register_ops(const struct frontswap_ops *ops);
> -
> -extern void frontswap_init(unsigned type, unsigned long *map);
> -extern int __frontswap_store(struct page *page);
> -extern int __frontswap_load(struct page *page);
> -extern void __frontswap_invalidate_page(unsigned, pgoff_t);
> -extern void __frontswap_invalidate_area(unsigned);
> -
> -#ifdef CONFIG_FRONTSWAP
> -extern struct static_key_false frontswap_enabled_key;
> -
> -static inline bool frontswap_enabled(void)
> -{
> -       return static_branch_unlikely(&frontswap_enabled_key);
> -}
> -
> -static inline void frontswap_map_set(struct swap_info_struct *p,
> -                                    unsigned long *map)
> -{
> -       p->frontswap_map =3D map;
> -}
> -
> -static inline unsigned long *frontswap_map_get(struct swap_info_struct *=
p)
> -{
> -       return p->frontswap_map;
> -}
> -#else
> -/* all inline routines become no-ops and all externs are ignored */
> -
> -static inline bool frontswap_enabled(void)
> -{
> -       return false;
> -}
> -
> -static inline void frontswap_map_set(struct swap_info_struct *p,
> -                                    unsigned long *map)
> -{
> -}
> -
> -static inline unsigned long *frontswap_map_get(struct swap_info_struct *=
p)
> -{
> -       return NULL;
> -}
> -#endif
> -
> -static inline int frontswap_store(struct page *page)
> -{
> -       if (frontswap_enabled())
> -               return __frontswap_store(page);
> -
> -       return -1;
> -}
> -
> -static inline int frontswap_load(struct page *page)
> -{
> -       if (frontswap_enabled())
> -               return __frontswap_load(page);
> -
> -       return -1;
> -}
> -
> -static inline void frontswap_invalidate_page(unsigned type, pgoff_t offs=
et)
> -{
> -       if (frontswap_enabled())
> -               __frontswap_invalidate_page(type, offset);
> -}
> -
> -static inline void frontswap_invalidate_area(unsigned type)
> -{
> -       if (frontswap_enabled())
> -               __frontswap_invalidate_area(type);
> -}
> -
> -#endif /* _LINUX_FRONTSWAP_H */
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 456546443f1f..bb5adc604144 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -302,10 +302,6 @@ struct swap_info_struct {
>         struct file *swap_file;         /* seldom referenced */
>         unsigned int old_block_size;    /* seldom referenced */
>         struct completion comp;         /* seldom referenced */
> -#ifdef CONFIG_FRONTSWAP
> -       unsigned long *frontswap_map;   /* frontswap in-use, one bit per =
page */
> -       atomic_t frontswap_pages;       /* frontswap pages in-use counter=
 */
> -#endif
>         spinlock_t lock;                /*
>                                          * protect map scan related field=
s like
>                                          * swap_map, lowest_bit, highest_=
bit,
> @@ -630,11 +626,6 @@ static inline int mem_cgroup_swappiness(struct mem_c=
group *mem)
>  }
>  #endif
>
> -#ifdef CONFIG_ZSWAP
> -extern u64 zswap_pool_total_size;
> -extern atomic_t zswap_stored_pages;
> -#endif
> -
>  #if defined(CONFIG_SWAP) && defined(CONFIG_MEMCG) && defined(CONFIG_BLK_=
CGROUP)
>  void __folio_throttle_swaprate(struct folio *folio, gfp_t gfp);
>  static inline void folio_throttle_swaprate(struct folio *folio, gfp_t gf=
p)
> diff --git a/include/linux/swapfile.h b/include/linux/swapfile.h
> index 7ed529a77c5b..99e3ed469e88 100644
> --- a/include/linux/swapfile.h
> +++ b/include/linux/swapfile.h
> @@ -2,11 +2,6 @@
>  #ifndef _LINUX_SWAPFILE_H
>  #define _LINUX_SWAPFILE_H
>
> -/*
> - * these were static in swapfile.c but frontswap.c needs them and we don=
't
> - * want to expose them to the dozens of source files that include swap.h
> - */
> -extern struct swap_info_struct *swap_info[];
>  extern unsigned long generic_max_swapfile_size(void);
>  unsigned long arch_max_swapfile_size(void);
>
> diff --git a/include/linux/zswap.h b/include/linux/zswap.h
> new file mode 100644
> index 000000000000..850c377d9b6d
> --- /dev/null
> +++ b/include/linux/zswap.h
> @@ -0,0 +1,37 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _LINUX_ZSWAP_H
> +#define _LINUX_ZSWAP_H
> +
> +#include <linux/types.h>
> +#include <linux/mm_types.h>
> +
> +extern u64 zswap_pool_total_size;
> +extern atomic_t zswap_stored_pages;
> +
> +#ifdef CONFIG_ZSWAP
> +
> +bool zswap_store(struct page *page);
> +bool zswap_load(struct page *page);
> +void zswap_invalidate(int type, pgoff_t offset);
> +void zswap_swapon(int type);
> +void zswap_swapoff(int type);
> +
> +#else
> +
> +static inline bool zswap_store(struct page *page)
> +{
> +       return false;
> +}
> +
> +static inline bool zswap_load(struct page *page)
> +{
> +       return false;
> +}
> +
> +static inline void zswap_invalidate(int type, pgoff_t offset) {}
> +static inline void zswap_swapon(int type) {}
> +static inline void zswap_swapoff(int type) {}
> +
> +#endif
> +
> +#endif /* _LINUX_ZSWAP_H */
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 09130434e30d..4ebc095590f6 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -25,7 +25,6 @@ menuconfig SWAP
>  config ZSWAP
>         bool "Compressed cache for swap pages"
>         depends on SWAP
> -       select FRONTSWAP
>         select CRYPTO
>         select ZPOOL
>         help
> @@ -870,9 +869,6 @@ config USE_PERCPU_NUMA_NODE_ID
>  config HAVE_SETUP_PER_CPU_AREA
>         bool
>
> -config FRONTSWAP
> -       bool
> -
>  config CMA
>         bool "Contiguous Memory Allocator"
>         depends on MMU
> diff --git a/mm/Makefile b/mm/Makefile
> index 678530a07326..e6d9a1d5e84d 100644
> --- a/mm/Makefile
> +++ b/mm/Makefile
> @@ -72,7 +72,6 @@ ifdef CONFIG_MMU
>  endif
>
>  obj-$(CONFIG_SWAP)     +=3D page_io.o swap_state.o swapfile.o swap_slots=
.o
> -obj-$(CONFIG_FRONTSWAP)        +=3D frontswap.o
>  obj-$(CONFIG_ZSWAP)    +=3D zswap.o
>  obj-$(CONFIG_HAS_DMA)  +=3D dmapool.o
>  obj-$(CONFIG_HUGETLBFS)        +=3D hugetlb.o
> diff --git a/mm/frontswap.c b/mm/frontswap.c
> deleted file mode 100644
> index 2fb5df3384b8..000000000000
> --- a/mm/frontswap.c
> +++ /dev/null
> @@ -1,283 +0,0 @@
> -// SPDX-License-Identifier: GPL-2.0-only
> -/*
> - * Frontswap frontend
> - *
> - * This code provides the generic "frontend" layer to call a matching
> - * "backend" driver implementation of frontswap.  See
> - * Documentation/mm/frontswap.rst for more information.
> - *
> - * Copyright (C) 2009-2012 Oracle Corp.  All rights reserved.
> - * Author: Dan Magenheimer
> - */
> -
> -#include <linux/mman.h>
> -#include <linux/swap.h>
> -#include <linux/swapops.h>
> -#include <linux/security.h>
> -#include <linux/module.h>
> -#include <linux/debugfs.h>
> -#include <linux/frontswap.h>
> -#include <linux/swapfile.h>
> -
> -DEFINE_STATIC_KEY_FALSE(frontswap_enabled_key);
> -
> -/*
> - * frontswap_ops are added by frontswap_register_ops, and provide the
> - * frontswap "backend" implementation functions.  Multiple implementatio=
ns
> - * may be registered, but implementations can never deregister.  This
> - * is a simple singly-linked list of all registered implementations.
> - */
> -static const struct frontswap_ops *frontswap_ops __read_mostly;
> -
> -#ifdef CONFIG_DEBUG_FS
> -/*
> - * Counters available via /sys/kernel/debug/frontswap (if debugfs is
> - * properly configured).  These are for information only so are not prot=
ected
> - * against increment races.
> - */
> -static u64 frontswap_loads;
> -static u64 frontswap_succ_stores;
> -static u64 frontswap_failed_stores;
> -static u64 frontswap_invalidates;
> -
> -static inline void inc_frontswap_loads(void)
> -{
> -       data_race(frontswap_loads++);
> -}
> -static inline void inc_frontswap_succ_stores(void)
> -{
> -       data_race(frontswap_succ_stores++);
> -}
> -static inline void inc_frontswap_failed_stores(void)
> -{
> -       data_race(frontswap_failed_stores++);
> -}
> -static inline void inc_frontswap_invalidates(void)
> -{
> -       data_race(frontswap_invalidates++);
> -}
> -#else
> -static inline void inc_frontswap_loads(void) { }
> -static inline void inc_frontswap_succ_stores(void) { }
> -static inline void inc_frontswap_failed_stores(void) { }
> -static inline void inc_frontswap_invalidates(void) { }
> -#endif
> -
> -/*
> - * Due to the asynchronous nature of the backends loading potentially
> - * _after_ the swap system has been activated, we have chokepoints
> - * on all frontswap functions to not call the backend until the backend
> - * has registered.
> - *
> - * This would not guards us against the user deciding to call swapoff ri=
ght as
> - * we are calling the backend to initialize (so swapon is in action).
> - * Fortunately for us, the swapon_mutex has been taken by the callee so =
we are
> - * OK. The other scenario where calls to frontswap_store (called via
> - * swap_writepage) is racing with frontswap_invalidate_area (called via
> - * swapoff) is again guarded by the swap subsystem.
> - *
> - * While no backend is registered all calls to frontswap_[store|load|
> - * invalidate_area|invalidate_page] are ignored or fail.
> - *
> - * The time between the backend being registered and the swap file syste=
m
> - * calling the backend (via the frontswap_* functions) is indeterminate =
as
> - * frontswap_ops is not atomic_t (or a value guarded by a spinlock).
> - * That is OK as we are comfortable missing some of these calls to the n=
ewly
> - * registered backend.
> - *
> - * Obviously the opposite (unloading the backend) must be done after all
> - * the frontswap_[store|load|invalidate_area|invalidate_page] start
> - * ignoring or failing the requests.  However, there is currently no way
> - * to unload a backend once it is registered.
> - */
> -
> -/*
> - * Register operations for frontswap
> - */
> -int frontswap_register_ops(const struct frontswap_ops *ops)
> -{
> -       if (frontswap_ops)
> -               return -EINVAL;
> -
> -       frontswap_ops =3D ops;
> -       static_branch_inc(&frontswap_enabled_key);
> -       return 0;
> -}
> -
> -/*
> - * Called when a swap device is swapon'd.
> - */
> -void frontswap_init(unsigned type, unsigned long *map)
> -{
> -       struct swap_info_struct *sis =3D swap_info[type];
> -
> -       VM_BUG_ON(sis =3D=3D NULL);
> -
> -       /*
> -        * p->frontswap is a bitmap that we MUST have to figure out which=
 page
> -        * has gone in frontswap. Without it there is no point of continu=
ing.
> -        */
> -       if (WARN_ON(!map))
> -               return;
> -       /*
> -        * Irregardless of whether the frontswap backend has been loaded
> -        * before this function or it will be later, we _MUST_ have the
> -        * p->frontswap set to something valid to work properly.
> -        */
> -       frontswap_map_set(sis, map);
> -
> -       if (!frontswap_enabled())
> -               return;
> -       frontswap_ops->init(type);
> -}
> -
> -static bool __frontswap_test(struct swap_info_struct *sis,
> -                               pgoff_t offset)
> -{
> -       if (sis->frontswap_map)
> -               return test_bit(offset, sis->frontswap_map);
> -       return false;
> -}
> -
> -static inline void __frontswap_set(struct swap_info_struct *sis,
> -                                  pgoff_t offset)
> -{
> -       set_bit(offset, sis->frontswap_map);
> -       atomic_inc(&sis->frontswap_pages);
> -}
> -
> -static inline void __frontswap_clear(struct swap_info_struct *sis,
> -                                    pgoff_t offset)
> -{
> -       clear_bit(offset, sis->frontswap_map);
> -       atomic_dec(&sis->frontswap_pages);
> -}
> -
> -/*
> - * "Store" data from a page to frontswap and associate it with the page'=
s
> - * swaptype and offset.  Page must be locked and in the swap cache.
> - * If frontswap already contains a page with matching swaptype and
> - * offset, the frontswap implementation may either overwrite the data an=
d
> - * return success or invalidate the page from frontswap and return failu=
re.
> - */
> -int __frontswap_store(struct page *page)
> -{
> -       int ret =3D -1;
> -       swp_entry_t entry =3D { .val =3D page_private(page), };
> -       int type =3D swp_type(entry);
> -       struct swap_info_struct *sis =3D swap_info[type];
> -       pgoff_t offset =3D swp_offset(entry);
> -
> -       VM_BUG_ON(!frontswap_ops);
> -       VM_BUG_ON(!PageLocked(page));
> -       VM_BUG_ON(sis =3D=3D NULL);
> -
> -       /*
> -        * If a dup, we must remove the old page first; we can't leave th=
e
> -        * old page no matter if the store of the new page succeeds or fa=
ils,
> -        * and we can't rely on the new page replacing the old page as we=
 may
> -        * not store to the same implementation that contains the old pag=
e.
> -        */
> -       if (__frontswap_test(sis, offset)) {
> -               __frontswap_clear(sis, offset);
> -               frontswap_ops->invalidate_page(type, offset);
> -       }
> -
> -       ret =3D frontswap_ops->store(type, offset, page);
> -       if (ret =3D=3D 0) {
> -               __frontswap_set(sis, offset);
> -               inc_frontswap_succ_stores();
> -       } else {
> -               inc_frontswap_failed_stores();
> -       }
> -
> -       return ret;
> -}
> -
> -/*
> - * "Get" data from frontswap associated with swaptype and offset that we=
re
> - * specified when the data was put to frontswap and use it to fill the
> - * specified page with data. Page must be locked and in the swap cache.
> - */
> -int __frontswap_load(struct page *page)
> -{
> -       int ret =3D -1;
> -       swp_entry_t entry =3D { .val =3D page_private(page), };
> -       int type =3D swp_type(entry);
> -       struct swap_info_struct *sis =3D swap_info[type];
> -       pgoff_t offset =3D swp_offset(entry);
> -       bool exclusive =3D false;
> -
> -       VM_BUG_ON(!frontswap_ops);
> -       VM_BUG_ON(!PageLocked(page));
> -       VM_BUG_ON(sis =3D=3D NULL);
> -
> -       if (!__frontswap_test(sis, offset))
> -               return -1;
> -
> -       /* Try loading from each implementation, until one succeeds. */
> -       ret =3D frontswap_ops->load(type, offset, page, &exclusive);
> -       if (ret =3D=3D 0) {
> -               inc_frontswap_loads();
> -               if (exclusive) {
> -                       SetPageDirty(page);
> -                       __frontswap_clear(sis, offset);
> -               }
> -       }
> -       return ret;
> -}
> -
> -/*
> - * Invalidate any data from frontswap associated with the specified swap=
type
> - * and offset so that a subsequent "get" will fail.
> - */
> -void __frontswap_invalidate_page(unsigned type, pgoff_t offset)
> -{
> -       struct swap_info_struct *sis =3D swap_info[type];
> -
> -       VM_BUG_ON(!frontswap_ops);
> -       VM_BUG_ON(sis =3D=3D NULL);
> -
> -       if (!__frontswap_test(sis, offset))
> -               return;
> -
> -       frontswap_ops->invalidate_page(type, offset);
> -       __frontswap_clear(sis, offset);
> -       inc_frontswap_invalidates();
> -}
> -
> -/*
> - * Invalidate all data from frontswap associated with all offsets for th=
e
> - * specified swaptype.
> - */
> -void __frontswap_invalidate_area(unsigned type)
> -{
> -       struct swap_info_struct *sis =3D swap_info[type];
> -
> -       VM_BUG_ON(!frontswap_ops);
> -       VM_BUG_ON(sis =3D=3D NULL);
> -
> -       if (sis->frontswap_map =3D=3D NULL)
> -               return;
> -
> -       frontswap_ops->invalidate_area(type);
> -       atomic_set(&sis->frontswap_pages, 0);
> -       bitmap_zero(sis->frontswap_map, sis->max);
> -}
> -
> -static int __init init_frontswap(void)
> -{
> -#ifdef CONFIG_DEBUG_FS
> -       struct dentry *root =3D debugfs_create_dir("frontswap", NULL);
> -       if (root =3D=3D NULL)
> -               return -ENXIO;
> -       debugfs_create_u64("loads", 0444, root, &frontswap_loads);
> -       debugfs_create_u64("succ_stores", 0444, root, &frontswap_succ_sto=
res);
> -       debugfs_create_u64("failed_stores", 0444, root,
> -                          &frontswap_failed_stores);
> -       debugfs_create_u64("invalidates", 0444, root, &frontswap_invalida=
tes);
> -#endif
> -       return 0;
> -}
> -
> -module_init(init_frontswap);
> diff --git a/mm/page_io.c b/mm/page_io.c
> index 684cd3c7b59b..32afc2a52982 100644
> --- a/mm/page_io.c
> +++ b/mm/page_io.c
> @@ -19,12 +19,12 @@
>  #include <linux/bio.h>
>  #include <linux/swapops.h>
>  #include <linux/writeback.h>
> -#include <linux/frontswap.h>
>  #include <linux/blkdev.h>
>  #include <linux/psi.h>
>  #include <linux/uio.h>
>  #include <linux/sched/task.h>
>  #include <linux/delayacct.h>
> +#include <linux/zswap.h>
>  #include "swap.h"
>
>  static void __end_swap_bio_write(struct bio *bio)
> @@ -198,7 +198,7 @@ int swap_writepage(struct page *page, struct writebac=
k_control *wbc)
>                 folio_unlock(folio);
>                 return ret;
>         }
> -       if (frontswap_store(&folio->page) =3D=3D 0) {
> +       if (zswap_store(&folio->page)) {
>                 folio_start_writeback(folio);
>                 folio_unlock(folio);
>                 folio_end_writeback(folio);
> @@ -515,7 +515,7 @@ void swap_readpage(struct page *page, bool synchronou=
s, struct swap_iocb **plug)
>         }
>         delayacct_swapin_start();
>
> -       if (frontswap_load(page) =3D=3D 0) {
> +       if (zswap_load(page)) {
>                 SetPageUptodate(page);
>                 unlock_page(page);
>         } else if (data_race(sis->flags & SWP_FS_OPS)) {
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 8e6dde68b389..38cd4dc4b2e7 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -35,13 +35,13 @@
>  #include <linux/memcontrol.h>
>  #include <linux/poll.h>
>  #include <linux/oom.h>
> -#include <linux/frontswap.h>
>  #include <linux/swapfile.h>
>  #include <linux/export.h>
>  #include <linux/swap_slots.h>
>  #include <linux/sort.h>
>  #include <linux/completion.h>
>  #include <linux/suspend.h>
> +#include <linux/zswap.h>
>
>  #include <asm/tlbflush.h>
>  #include <linux/swapops.h>
> @@ -95,7 +95,7 @@ static PLIST_HEAD(swap_active_head);
>  static struct plist_head *swap_avail_heads;
>  static DEFINE_SPINLOCK(swap_avail_lock);
>
> -struct swap_info_struct *swap_info[MAX_SWAPFILES];
> +static struct swap_info_struct *swap_info[MAX_SWAPFILES];
>
>  static DEFINE_MUTEX(swapon_mutex);
>
> @@ -746,7 +746,7 @@ static void swap_range_free(struct swap_info_struct *=
si, unsigned long offset,
>                 swap_slot_free_notify =3D NULL;
>         while (offset <=3D end) {
>                 arch_swap_invalidate_page(si->type, offset);
> -               frontswap_invalidate_page(si->type, offset);
> +               zswap_invalidate(si->type, offset);
>                 if (swap_slot_free_notify)
>                         swap_slot_free_notify(si->bdev, offset);
>                 offset++;
> @@ -2335,11 +2335,10 @@ static void _enable_swap_info(struct swap_info_st=
ruct *p)
>
>  static void enable_swap_info(struct swap_info_struct *p, int prio,
>                                 unsigned char *swap_map,
> -                               struct swap_cluster_info *cluster_info,
> -                               unsigned long *frontswap_map)
> +                               struct swap_cluster_info *cluster_info)
>  {
> -       if (IS_ENABLED(CONFIG_FRONTSWAP))
> -               frontswap_init(p->type, frontswap_map);
> +       zswap_swapon(p->type);
> +
>         spin_lock(&swap_lock);
>         spin_lock(&p->lock);
>         setup_swap_info(p, prio, swap_map, cluster_info);
> @@ -2382,7 +2381,6 @@ SYSCALL_DEFINE1(swapoff, const char __user *, speci=
alfile)
>         struct swap_info_struct *p =3D NULL;
>         unsigned char *swap_map;
>         struct swap_cluster_info *cluster_info;
> -       unsigned long *frontswap_map;
>         struct file *swap_file, *victim;
>         struct address_space *mapping;
>         struct inode *inode;
> @@ -2507,12 +2505,10 @@ SYSCALL_DEFINE1(swapoff, const char __user *, spe=
cialfile)
>         p->swap_map =3D NULL;
>         cluster_info =3D p->cluster_info;
>         p->cluster_info =3D NULL;
> -       frontswap_map =3D frontswap_map_get(p);
>         spin_unlock(&p->lock);
>         spin_unlock(&swap_lock);
>         arch_swap_invalidate_area(p->type);
> -       frontswap_invalidate_area(p->type);
> -       frontswap_map_set(p, NULL);
> +       zswap_swapoff(p->type);
>         mutex_unlock(&swapon_mutex);
>         free_percpu(p->percpu_cluster);
>         p->percpu_cluster =3D NULL;
> @@ -2520,7 +2516,6 @@ SYSCALL_DEFINE1(swapoff, const char __user *, speci=
alfile)
>         p->cluster_next_cpu =3D NULL;
>         vfree(swap_map);
>         kvfree(cluster_info);
> -       kvfree(frontswap_map);
>         /* Destroy swap account information */
>         swap_cgroup_swapoff(p->type);
>         exit_swap_address_space(p->type);
> @@ -2987,7 +2982,6 @@ SYSCALL_DEFINE2(swapon, const char __user *, specia=
lfile, int, swap_flags)
>         unsigned long maxpages;
>         unsigned char *swap_map =3D NULL;
>         struct swap_cluster_info *cluster_info =3D NULL;
> -       unsigned long *frontswap_map =3D NULL;
>         struct page *page =3D NULL;
>         struct inode *inode =3D NULL;
>         bool inced_nr_rotate_swap =3D false;
> @@ -3127,11 +3121,6 @@ SYSCALL_DEFINE2(swapon, const char __user *, speci=
alfile, int, swap_flags)
>                 error =3D nr_extents;
>                 goto bad_swap_unlock_inode;
>         }
> -       /* frontswap enabled? set up bit-per-page map for frontswap */
> -       if (IS_ENABLED(CONFIG_FRONTSWAP))
> -               frontswap_map =3D kvcalloc(BITS_TO_LONGS(maxpages),
> -                                        sizeof(long),
> -                                        GFP_KERNEL);
>
>         if ((swap_flags & SWAP_FLAG_DISCARD) &&
>             p->bdev && bdev_max_discard_sectors(p->bdev)) {
> @@ -3184,16 +3173,15 @@ SYSCALL_DEFINE2(swapon, const char __user *, spec=
ialfile, int, swap_flags)
>         if (swap_flags & SWAP_FLAG_PREFER)
>                 prio =3D
>                   (swap_flags & SWAP_FLAG_PRIO_MASK) >> SWAP_FLAG_PRIO_SH=
IFT;
> -       enable_swap_info(p, prio, swap_map, cluster_info, frontswap_map);
> +       enable_swap_info(p, prio, swap_map, cluster_info);
>
> -       pr_info("Adding %uk swap on %s.  Priority:%d extents:%d across:%l=
luk %s%s%s%s%s\n",
> +       pr_info("Adding %uk swap on %s.  Priority:%d extents:%d across:%l=
luk %s%s%s%s\n",
>                 p->pages<<(PAGE_SHIFT-10), name->name, p->prio,
>                 nr_extents, (unsigned long long)span<<(PAGE_SHIFT-10),
>                 (p->flags & SWP_SOLIDSTATE) ? "SS" : "",
>                 (p->flags & SWP_DISCARDABLE) ? "D" : "",
>                 (p->flags & SWP_AREA_DISCARD) ? "s" : "",
> -               (p->flags & SWP_PAGE_DISCARD) ? "c" : "",
> -               (frontswap_map) ? "FS" : "");
> +               (p->flags & SWP_PAGE_DISCARD) ? "c" : "");
>
>         mutex_unlock(&swapon_mutex);
>         atomic_inc(&proc_poll_event);
> @@ -3223,7 +3211,6 @@ SYSCALL_DEFINE2(swapon, const char __user *, specia=
lfile, int, swap_flags)
>         spin_unlock(&swap_lock);
>         vfree(swap_map);
>         kvfree(cluster_info);
> -       kvfree(frontswap_map);
>         if (inced_nr_rotate_swap)
>                 atomic_dec(&nr_rotate_swap);
>         if (swap_file)
> diff --git a/mm/zswap.c b/mm/zswap.c
> index 62195f72bf56..1b0128060792 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -2,7 +2,7 @@
>  /*
>   * zswap.c - zswap driver file
>   *
> - * zswap is a backend for frontswap that takes pages that are in the pro=
cess
> + * zswap is a cache that takes pages that are in the process
>   * of being swapped out and attempts to compress and store them in a
>   * RAM-based memory pool.  This can result in a significant I/O reductio=
n on
>   * the swap device and, in the case where decompressing from RAM is fast=
er
> @@ -20,7 +20,6 @@
>  #include <linux/spinlock.h>
>  #include <linux/types.h>
>  #include <linux/atomic.h>
> -#include <linux/frontswap.h>
>  #include <linux/rbtree.h>
>  #include <linux/swap.h>
>  #include <linux/crypto.h>
> @@ -1061,7 +1060,7 @@ static int zswap_get_swap_cache_page(swp_entry_t en=
try,
>   *
>   * This can be thought of as a "resumed writeback" of the page
>   * to the swap device.  We are basically resuming the same swap
> - * writeback path that was intercepted with the frontswap_store()
> + * writeback path that was intercepted with the zswap_store()
>   * in the first place.  After the page has been decompressed into
>   * the swap cache, the compressed version stored by zswap can be
>   * freed.
> @@ -1201,36 +1200,33 @@ static void zswap_fill_page(void *ptr, unsigned l=
ong value)
>         memset_l(page, value, PAGE_SIZE / sizeof(unsigned long));
>  }
>
> -/*********************************
> -* frontswap hooks
> -**********************************/
> -/* attempts to compress and store an single page */
> -static int zswap_frontswap_store(unsigned type, pgoff_t offset,
> -                               struct page *page)
> +bool zswap_store(struct page *page)
>  {
> +       swp_entry_t swp =3D { .val =3D page_private(page), };
> +       int type =3D swp_type(swp);
> +       pgoff_t offset =3D swp_offset(swp);
>         struct zswap_tree *tree =3D zswap_trees[type];
>         struct zswap_entry *entry, *dupentry;
>         struct scatterlist input, output;
>         struct crypto_acomp_ctx *acomp_ctx;
>         struct obj_cgroup *objcg =3D NULL;
>         struct zswap_pool *pool;
> -       int ret;
>         unsigned int dlen =3D PAGE_SIZE;
>         unsigned long handle, value;
>         char *buf;
>         u8 *src, *dst;
>         gfp_t gfp;
> +       int ret;
> +
> +       VM_WARN_ON_ONCE(!PageLocked(page));
> +       VM_WARN_ON_ONCE(!PageSwapCache(page));
>
>         /* THP isn't supported */
> -       if (PageTransHuge(page)) {
> -               ret =3D -EINVAL;
> -               goto reject;
> -       }
> +       if (PageTransHuge(page))
> +               return false;
>
> -       if (!zswap_enabled || !tree) {
> -               ret =3D -ENODEV;
> -               goto reject;
> -       }
> +       if (!zswap_enabled || !tree)
> +               return false;
>
>         /*
>          * XXX: zswap reclaim does not work with cgroups yet. Without a
> @@ -1238,10 +1234,8 @@ static int zswap_frontswap_store(unsigned type, pg=
off_t offset,
>          * local cgroup limits.
>          */
>         objcg =3D get_obj_cgroup_from_page(page);
> -       if (objcg && !obj_cgroup_may_zswap(objcg)) {
> -               ret =3D -ENOMEM;
> +       if (objcg && !obj_cgroup_may_zswap(objcg))
>                 goto reject;
> -       }
>
>         /* reclaim space if needed */
>         if (zswap_is_full()) {
> @@ -1251,10 +1245,9 @@ static int zswap_frontswap_store(unsigned type, pg=
off_t offset,
>         }
>
>         if (zswap_pool_reached_full) {
> -              if (!zswap_can_accept()) {
> -                       ret =3D -ENOMEM;
> +              if (!zswap_can_accept())
>                         goto shrink;
> -               } else
> +               else
>                         zswap_pool_reached_full =3D false;
>         }
>
> @@ -1262,7 +1255,6 @@ static int zswap_frontswap_store(unsigned type, pgo=
ff_t offset,
>         entry =3D zswap_entry_cache_alloc(GFP_KERNEL);
>         if (!entry) {
>                 zswap_reject_kmemcache_fail++;
> -               ret =3D -ENOMEM;
>                 goto reject;
>         }
>
> @@ -1279,17 +1271,13 @@ static int zswap_frontswap_store(unsigned type, p=
goff_t offset,
>                 kunmap_atomic(src);
>         }
>
> -       if (!zswap_non_same_filled_pages_enabled) {
> -               ret =3D -EINVAL;
> +       if (!zswap_non_same_filled_pages_enabled)
>                 goto freepage;
> -       }
>
>         /* if entry is successfully added, it keeps the reference */
>         entry->pool =3D zswap_pool_current_get();
> -       if (!entry->pool) {
> -               ret =3D -EINVAL;
> +       if (!entry->pool)
>                 goto freepage;
> -       }
>
>         /* compress */
>         acomp_ctx =3D raw_cpu_ptr(entry->pool->acomp_ctx);
> @@ -1309,19 +1297,17 @@ static int zswap_frontswap_store(unsigned type, p=
goff_t offset,
>          * synchronous in fact.
>          * Theoretically, acomp supports users send multiple acomp reques=
ts in one
>          * acomp instance, then get those requests done simultaneously. b=
ut in this
> -        * case, frontswap actually does store and load page by page, the=
re is no
> +        * case, zswap actually does store and load page by page, there i=
s no
>          * existing method to send the second page before the first page =
is done
> -        * in one thread doing frontswap.
> +        * in one thread doing zwap.
>          * but in different threads running on different cpu, we have dif=
ferent
>          * acomp instance, so multiple threads can do (de)compression in =
parallel.
>          */
>         ret =3D crypto_wait_req(crypto_acomp_compress(acomp_ctx->req), &a=
comp_ctx->wait);
>         dlen =3D acomp_ctx->req->dlen;
>
> -       if (ret) {
> -               ret =3D -EINVAL;
> +       if (ret)
>                 goto put_dstmem;
> -       }
>
>         /* store */
>         gfp =3D __GFP_NORETRY | __GFP_NOWARN | __GFP_KSWAPD_RECLAIM;
> @@ -1356,15 +1342,12 @@ static int zswap_frontswap_store(unsigned type, p=
goff_t offset,
>
>         /* map */
>         spin_lock(&tree->lock);
> -       do {
> -               ret =3D zswap_rb_insert(&tree->rbroot, entry, &dupentry);
> -               if (ret =3D=3D -EEXIST) {
> -                       zswap_duplicate_entry++;
> -                       /* remove from rbtree */
> -                       zswap_rb_erase(&tree->rbroot, dupentry);
> -                       zswap_entry_put(tree, dupentry);
> -               }
> -       } while (ret =3D=3D -EEXIST);
> +       while (zswap_rb_insert(&tree->rbroot, entry, &dupentry) =3D=3D -E=
EXIST) {
> +               zswap_duplicate_entry++;
> +               /* remove from rbtree */
> +               zswap_rb_erase(&tree->rbroot, dupentry);
> +               zswap_entry_put(tree, dupentry);
> +       }
>         if (entry->length) {
>                 spin_lock(&entry->pool->lru_lock);
>                 list_add(&entry->lru, &entry->pool->lru);
> @@ -1377,7 +1360,7 @@ static int zswap_frontswap_store(unsigned type, pgo=
ff_t offset,
>         zswap_update_total_size();
>         count_vm_event(ZSWPOUT);
>
> -       return 0;
> +       return true;
>
>  put_dstmem:
>         mutex_unlock(acomp_ctx->mutex);
> @@ -1387,30 +1370,30 @@ static int zswap_frontswap_store(unsigned type, p=
goff_t offset,
>  reject:
>         if (objcg)
>                 obj_cgroup_put(objcg);
> -       return ret;
> +       return false;
>
>  shrink:
>         pool =3D zswap_pool_last_get();
>         if (pool)
>                 queue_work(shrink_wq, &pool->shrink_work);
> -       ret =3D -ENOMEM;
>         goto reject;
>  }
>
> -/*
> - * returns 0 if the page was successfully decompressed
> - * return -1 on entry not found or error
> -*/
> -static int zswap_frontswap_load(unsigned type, pgoff_t offset,
> -                               struct page *page, bool *exclusive)
> +bool zswap_load(struct page *page)
>  {
> +       swp_entry_t swp =3D { .val =3D page_private(page), };
> +       int type =3D swp_type(swp);
> +       pgoff_t offset =3D swp_offset(swp);
>         struct zswap_tree *tree =3D zswap_trees[type];
>         struct zswap_entry *entry;
>         struct scatterlist input, output;
>         struct crypto_acomp_ctx *acomp_ctx;
>         u8 *src, *dst, *tmp;
>         unsigned int dlen;
> -       int ret;
> +       bool ret;
> +
> +       VM_WARN_ON_ONCE(!PageLocked(page));
> +       VM_WARN_ON_ONCE(!PageSwapCache(page));
>
>         /* find */
>         spin_lock(&tree->lock);
> @@ -1418,7 +1401,7 @@ static int zswap_frontswap_load(unsigned type, pgof=
f_t offset,
>         if (!entry) {
>                 /* entry was written back */
>                 spin_unlock(&tree->lock);
> -               return -1;
> +               return false;
>         }
>         spin_unlock(&tree->lock);
>
> @@ -1426,14 +1409,14 @@ static int zswap_frontswap_load(unsigned type, pg=
off_t offset,
>                 dst =3D kmap_atomic(page);
>                 zswap_fill_page(dst, entry->value);
>                 kunmap_atomic(dst);
> -               ret =3D 0;
> +               ret =3D true;
>                 goto stats;
>         }
>
>         if (!zpool_can_sleep_mapped(entry->pool->zpool)) {
>                 tmp =3D kmalloc(entry->length, GFP_KERNEL);
>                 if (!tmp) {
> -                       ret =3D -ENOMEM;
> +                       ret =3D false;
>                         goto freeentry;
>                 }
>         }
> @@ -1454,7 +1437,8 @@ static int zswap_frontswap_load(unsigned type, pgof=
f_t offset,
>         sg_init_table(&output, 1);
>         sg_set_page(&output, page, PAGE_SIZE, 0);
>         acomp_request_set_params(acomp_ctx->req, &input, &output, entry->=
length, dlen);
> -       ret =3D crypto_wait_req(crypto_acomp_decompress(acomp_ctx->req), =
&acomp_ctx->wait);
> +       if (crypto_wait_req(crypto_acomp_decompress(acomp_ctx->req), &aco=
mp_ctx->wait))
> +               WARN_ON(1);
>         mutex_unlock(acomp_ctx->mutex);
>
>         if (zpool_can_sleep_mapped(entry->pool->zpool))
> @@ -1462,16 +1446,16 @@ static int zswap_frontswap_load(unsigned type, pg=
off_t offset,
>         else
>                 kfree(tmp);
>
> -       BUG_ON(ret);
> +       ret =3D true;
>  stats:
>         count_vm_event(ZSWPIN);
>         if (entry->objcg)
>                 count_objcg_event(entry->objcg, ZSWPIN);
>  freeentry:
>         spin_lock(&tree->lock);
> -       if (!ret && zswap_exclusive_loads_enabled) {
> +       if (ret && zswap_exclusive_loads_enabled) {
>                 zswap_invalidate_entry(tree, entry);
> -               *exclusive =3D true;
> +               SetPageDirty(page);
>         } else if (entry->length) {
>                 spin_lock(&entry->pool->lru_lock);
>                 list_move(&entry->lru, &entry->pool->lru);
> @@ -1483,8 +1467,7 @@ static int zswap_frontswap_load(unsigned type, pgof=
f_t offset,
>         return ret;
>  }
>
> -/* frees an entry in zswap */
> -static void zswap_frontswap_invalidate_page(unsigned type, pgoff_t offse=
t)
> +void zswap_invalidate(int type, pgoff_t offset)
>  {
>         struct zswap_tree *tree =3D zswap_trees[type];
>         struct zswap_entry *entry;
> @@ -1501,8 +1484,22 @@ static void zswap_frontswap_invalidate_page(unsign=
ed type, pgoff_t offset)
>         spin_unlock(&tree->lock);
>  }
>
> -/* frees all zswap entries for the given swap type */
> -static void zswap_frontswap_invalidate_area(unsigned type)
> +void zswap_swapon(int type)
> +{
> +       struct zswap_tree *tree;
> +
> +       tree =3D kzalloc(sizeof(*tree), GFP_KERNEL);
> +       if (!tree) {
> +               pr_err("alloc failed, zswap disabled for swap type %d\n",=
 type);
> +               return;
> +       }
> +
> +       tree->rbroot =3D RB_ROOT;
> +       spin_lock_init(&tree->lock);
> +       zswap_trees[type] =3D tree;
> +}
> +
> +void zswap_swapoff(int type)
>  {
>         struct zswap_tree *tree =3D zswap_trees[type];
>         struct zswap_entry *entry, *n;
> @@ -1520,29 +1517,6 @@ static void zswap_frontswap_invalidate_area(unsign=
ed type)
>         zswap_trees[type] =3D NULL;
>  }
>
> -static void zswap_frontswap_init(unsigned type)
> -{
> -       struct zswap_tree *tree;
> -
> -       tree =3D kzalloc(sizeof(*tree), GFP_KERNEL);
> -       if (!tree) {
> -               pr_err("alloc failed, zswap disabled for swap type %d\n",=
 type);
> -               return;
> -       }
> -
> -       tree->rbroot =3D RB_ROOT;
> -       spin_lock_init(&tree->lock);
> -       zswap_trees[type] =3D tree;
> -}
> -
> -static const struct frontswap_ops zswap_frontswap_ops =3D {
> -       .store =3D zswap_frontswap_store,
> -       .load =3D zswap_frontswap_load,
> -       .invalidate_page =3D zswap_frontswap_invalidate_page,
> -       .invalidate_area =3D zswap_frontswap_invalidate_area,
> -       .init =3D zswap_frontswap_init
> -};
> -
>  /*********************************
>  * debugfs functions
>  **********************************/
> @@ -1631,16 +1605,11 @@ static int zswap_setup(void)
>         if (!shrink_wq)
>                 goto fallback_fail;
>
> -       ret =3D frontswap_register_ops(&zswap_frontswap_ops);
> -       if (ret)
> -               goto destroy_wq;
>         if (zswap_debugfs_init())
>                 pr_warn("debugfs initialization failed\n");
>         zswap_init_state =3D ZSWAP_INIT_SUCCEED;
>         return 0;
>
> -destroy_wq:
> -       destroy_workqueue(shrink_wq);
>  fallback_fail:
>         if (pool)
>                 zswap_pool_destroy(pool);
> --
> 2.41.0
>

LGTM (other than the Chinese documentation - I don't know
enough Chinese to review that).

This will save lots of boilerplate in future zswap changes. Thanks,
Johannes!

Acked-by: Nhat Pham <nphamcs@gmail.com>