From:   Nick Terrell <terrelln@fb.com>
To:     "Alex Xu (Hello71)" <alex_y_xu@yahoo.ca>
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>,
        "Sedat Dilek" <sedat.dilek@gmail.com>,
        Kees Cook <keescook@chromium.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-kbuild@vger.kernel.org" <linux-kbuild@vger.kernel.org>
Subject: Re: [PATCH v2 2/2] kbuild: pass --stream-size --no-content-size to
 zstd
Thread-Topic: [PATCH v2 2/2] kbuild: pass --stream-size --no-content-size to
 zstd
Thread-Index: AQHX4UhKidKPr3kbgE2o2YP10PuuiKwf/KCA
Date:   Fri, 3 Dec 2021 00:49:15 +0000
Message-ID: <A5D1EDEE-8979-43A1-B36C-9216602150EA@fb.com>
References: <20211124153105.155739-1-alex_y_xu@yahoo.ca>
 <20211124153105.155739-2-alex_y_xu@yahoo.ca>
In-Reply-To: <20211124153105.155739-2-alex_y_xu@yahoo.ca>
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> On Nov 24, 2021, at 7:31 AM, 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.
> 
> 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
> 

You can add:

Tested-by: Nick Terrell <terrelln@fb.com>
Reviewed-by: Nick Terrell <terrelln@fb.com>

Best,
Nick Terrell