linux-kernel - Re: [PATCH v2 2/2] kbuild: pass --stream-size --no-content-size to zstd

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Message-ID: <CA+icZUUZwGG-mJg26DOmadZksm4fMCE5QUmnX4ZghWxXzAy9HQ@mail.gmail.com>
Date:   Fri, 17 Dec 2021 09:51:36 +0100
From:   Sedat Dilek <sedat.dilek@...il.com>
To:     "Alex Xu (Hello71)" <alex_y_xu@...oo.ca>,
        Nick Terrell <terrelln@...com>
Cc:     Michael Forney <forney@...gle.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Ingo Molnar <mingo@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org
Subject: Re: [PATCH v2 2/2] kbuild: pass --stream-size --no-content-size to zstd

On Wed, Nov 24, 2021 at 4:30 PM Alex Xu (Hello71) <alex_y_xu@...oo.ca> wrote:
>
> Otherwise, it allocates 2 GB of memory at once. Even though the majority
> of this memory is never touched, the default heuristic overcommit
> refuses this request if less than 2 GB of RAM+swap is currently
> available. This results in "zstd: error 11 : Allocation error : not
> enough memory" and the kernel failing to build.
>
> When the size is specified, zstd will reduce the memory request
> appropriately. For typical kernel sizes of ~32 MB, the largest mmap
> request will be reduced to 512 MB, which will succeed on all but the
> smallest devices.
>
> For inputs around this size, --stream-size --no-content-size may
> slightly decrease the compressed size, or slightly increase it:
> https://github.com/facebook/zstd/issues/2848.
>

Hi Alex and Nick T.,

some questions:

Can I apply this patch as a single patch - without patch 1/2?

Is there an impact also on the kernel's ZRAM/ZSWAP support plus using
ZSTD as (de)comp-algo?

Here I have:

$ grep -i zstd /boot/config-5.15.7-1-amd64-clang13-lto | egrep -i 'zram|zswap'
CONFIG_ZSWAP_COMPRESSOR_DEFAULT_ZSTD=y
CONFIG_ZSWAP_COMPRESSOR_DEFAULT="zstd"
CONFIG_ZRAM_DEF_COMP_ZSTD=y
CONFIG_ZRAM_DEF_COMP="zstd"

Thanks.

Regards,
- Sedat -

> Signed-off-by: Alex Xu (Hello71) <alex_y_xu@...oo.ca>
> ---
>  scripts/Makefile.lib | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
> index ca901814986a..c98a82ca38e6 100644
> --- a/scripts/Makefile.lib
> +++ b/scripts/Makefile.lib
> @@ -466,12 +466,20 @@ quiet_cmd_xzmisc = XZMISC  $@
>  # single pass, so zstd doesn't need to allocate a window buffer. When streaming
>  # decompression is used, like initramfs decompression, zstd22 should likely not
>  # be used because it would require zstd to allocate a 128 MB buffer.
> +#
> +# --stream-size to reduce zstd memory usage (otherwise zstd -22 --ultra
> +# allocates, but does not use, 2 GB) and potentially improve compression.
> +#
> +# --no-content-size to save three bytes which we do not use (we use size_append).
> +
> +# zstd --stream-size is only supported since 1.4.4
> +zstd_stream_size = $(shell $(ZSTD) -1c --stream-size=0 --no-content-size </dev/null >/dev/null 2>&1 && printf '%s' '--stream-size=$(total_size) --no-content-size')
>
>  quiet_cmd_zstd = ZSTD    $@
> -      cmd_zstd = { cat $(real-prereqs) | $(ZSTD) -19; $(size_append); } > $@
> +      cmd_zstd = { cat $(real-prereqs) | $(ZSTD) $(zstd_stream_size) -19; $(size_append); } > $@
>
>  quiet_cmd_zstd22 = ZSTD22  $@
> -      cmd_zstd22 = { cat $(real-prereqs) | $(ZSTD) -22 --ultra; $(size_append); } > $@
> +      cmd_zstd22 = { cat $(real-prereqs) | $(ZSTD) $(zstd_stream_size) -22 --ultra; $(size_append); } > $@
>
>  # ASM offsets
>  # ---------------------------------------------------------------------------
> --
> 2.34.0
>