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Date:   Sun, 6 Nov 2022 16:33:51 +0300
From:   "Kirill A. Shutemov" <kirill@shutemov.name>
To:     Pasha Tatashin <pasha.tatashin@soleen.com>
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        hannes@cmpxchg.org, david@redhat.com, vincent.whitchurch@axis.com,
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        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-doc@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH] mm: anonymous shared memory naming
Message-ID: <20221106133351.ukb5quoizkkzyrge@box.shutemov.name>
References: <20221105025342.3130038-1-pasha.tatashin@soleen.com>
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On Sat, Nov 05, 2022 at 02:53:42AM +0000, Pasha Tatashin wrote:
> Since:
> commit 9a10064f5625 ("mm: add a field to store names for private anonymous
> memory")
> 
> We can set names for private anonymous memory but not for shared
> anonymous memory. However, naming shared anonymous memory just as
> useful for tracking purposes.
> 
> Extend the functionality to be able to set names for shared anon.
> 
> / [anon_shmem:<name>]      an anonymous shared memory mapping that has
>                            been named by userspace
> 
> Sample output:
>         share = mmap(NULL, SIZE, PROT_READ | PROT_WRITE,
>                      MAP_SHARED | MAP_ANONYMOUS, -1, 0);
>         rv = prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME,
>                    share, SIZE, "shared anon");
> 
> /proc/<pid>/maps (and smaps):
> 7fc8e2b4c000-7fc8f2b4c000 rw-s 00000000 00:01 1024
> /dev/zero (deleted) [anon_shmem:shared anon]
> 
> pmap $(pgrep a.out)
> 254:   pub/a.out
> 000056093fab2000      4K r---- a.out
> 000056093fab3000      4K r-x-- a.out
> 000056093fab4000      4K r---- a.out
> 000056093fab5000      4K r---- a.out
> 000056093fab6000      4K rw--- a.out
> 000056093fdeb000    132K rw---   [ anon ]
> 00007fc8e2b4c000 262144K rw-s- zero (deleted) [anon_shmem:shared anon]
> 
> Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> ---
>  Documentation/filesystems/proc.rst |  4 +++-
>  fs/proc/task_mmu.c                 |  7 ++++---
>  include/linux/mm.h                 |  2 ++
>  include/linux/mm_types.h           | 27 +++++++++++++--------------
>  mm/madvise.c                       |  7 ++-----
>  mm/shmem.c                         | 13 +++++++++++--
>  6 files changed, 35 insertions(+), 25 deletions(-)
> 
> diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
> index 898c99eae8e4..8f1e68460da5 100644
> --- a/Documentation/filesystems/proc.rst
> +++ b/Documentation/filesystems/proc.rst
> @@ -431,8 +431,10 @@ is not associated with a file:
>   [stack]                    the stack of the main process
>   [vdso]                     the "virtual dynamic shared object",
>                              the kernel system call handler
> - [anon:<name>]              an anonymous mapping that has been
> + [anon:<name>]              a private anonymous mapping that has been
>                              named by userspace
> + path [anon_shmem:<name>]   an anonymous shared memory mapping that has
> +                            been named by userspace

I expect it to break existing parsers. If the field starts with '/' it is
reasonable to assume the rest of the string to be a path, but it is not
the case now.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov