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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Sat, 25 Dec 2021 11:35:52 +0100
Message-ID: <CAMuHMdWcfnALb7G-5yiEZ-_s3gG_5NXgffk+hCcv24aFojwObQ@mail.gmail.com>
Subject: Re: [PATCH 01/13] mm: remove cleancache
To:     Christoph Hellwig <hch@lst.de>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        Hugh Dickins <hughd@google.com>,
        Seth Jennings <sjenning@redhat.com>,
        Dan Streetman <ddstreet@ieee.org>,
        Vitaly Wool <vitaly.wool@konsulko.com>,
        Matthew Wilcox <willy@infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux FS Devel <linux-fsdevel@vger.kernel.org>,
        Linux MM <linux-mm@kvack.org>
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On Sat, Dec 25, 2021 at 2:41 AM Christoph Hellwig <hch@lst.de> wrote:
> The cleancache subsystem is unused since the removal of Xen tmem driver
> in commit 814bbf49dcd0 ("xen: remove tmem driver").
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>

>  arch/m68k/configs/amiga_defconfig    |   1 -
>  arch/m68k/configs/apollo_defconfig   |   1 -
>  arch/m68k/configs/atari_defconfig    |   1 -
>  arch/m68k/configs/bvme6000_defconfig |   1 -
>  arch/m68k/configs/hp300_defconfig    |   1 -
>  arch/m68k/configs/mac_defconfig      |   1 -
>  arch/m68k/configs/multi_defconfig    |   1 -
>  arch/m68k/configs/mvme147_defconfig  |   1 -
>  arch/m68k/configs/mvme16x_defconfig  |   1 -
>  arch/m68k/configs/q40_defconfig      |   1 -
>  arch/m68k/configs/sun3_defconfig     |   1 -
>  arch/m68k/configs/sun3x_defconfig    |   1 -

Although this would be removed during the next refresh anyway:
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>

> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -444,28 +444,6 @@ config USE_PERCPU_NUMA_NODE_ID
>  config HAVE_SETUP_PER_CPU_AREA
>         bool
>
> -config CLEANCACHE
> -       bool "Enable cleancache driver to cache clean pages if tmem is present"
> -       help
> -         Cleancache can be thought of as a page-granularity victim cache
> -         for clean pages that the kernel's pageframe replacement algorithm
> -         (PFRA) would like to keep around, but can't since there isn't enough
> -         memory.  So when the PFRA "evicts" a page, it first attempts to use
> -         cleancache code to put the data contained in that page into
> -         "transcendent memory", memory that is not directly accessible or
> -         addressable by the kernel and is of unknown and possibly
> -         time-varying size.  And when a cleancache-enabled
> -         filesystem wishes to access a page in a file on disk, it first
> -         checks cleancache to see if it already contains it; if it does,
> -         the page is copied into the kernel and a disk access is avoided.
> -         When a transcendent memory driver is available (such as zcache or
> -         Xen transcendent memory), a significant I/O reduction
> -         may be achieved.  When none is available, all cleancache calls
> -         are reduced to a single pointer-compare-against-NULL resulting
> -         in a negligible performance hit.
> -
> -         If unsure, say Y to enable cleancache

Ah, the joy of good advice...

> -
>  config FRONTSWAP
>         bool "Enable frontswap to cache swap pages if tmem is present"
>         depends on SWAP

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds