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Reply-To: sedat.dilek@gmail.com
From:   Sedat Dilek <sedat.dilek@gmail.com>
Date:   Fri, 17 Dec 2021 14:44:06 +0100
Message-ID: <CA+icZUXLrENSgHJHy1Huy-tX-STpEQXyjQGO_fmdnhq7oMKhzA@mail.gmail.com>
Subject: Re: [PATCH v2 2/2] kbuild: pass --stream-size --no-content-size to zstd
To:     "Alex Xu (Hello71)" <alex_y_xu@yahoo.ca>,
        Nick Terrell <terrelln@fb.com>
Cc:     Michael Forney <forney@google.com>,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        Michal Marek <michal.lkml@markovi.net>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Ingo Molnar <mingo@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        linux-kernel@vger.kernel.org, linux-kbuild@vger.kernel.org
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On Fri, Dec 17, 2021 at 9:51 AM Sedat Dilek <sedat.dilek@gmail.com> wrote:
>
> On Wed, Nov 24, 2021 at 4:30 PM Alex Xu (Hello71) <alex_y_xu@yahoo.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"
>

$ egrep 'stream-size' build-log_5.15.9-1-amd64-clang13-lto.txt
49360:  { cat arch/x86/boot/compressed/vmlinux.bin
arch/x86/boot/compressed/vmlinux.relocs | zstd --stream-size=53340760
--no-content-size -22 --ultra; printf \130\352
\055\003; } > arch/x86/boot/compressed/vmlinux.bin.zst

Tested-by: Sedat Dilek <sedat.dilek@gmail.com>

- Sedat -

> Thanks.
>
> Regards,
> - Sedat -
>
> > Signed-off-by: Alex Xu (Hello71) <alex_y_xu@yahoo.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
> >