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

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Message-Id: <20211120165349.99908-2-alex_y_xu@yahoo.ca>
Date:   Sat, 20 Nov 2021 11:53:49 -0500
From:   "Alex Xu (Hello71)" <alex_y_xu@...oo.ca>
To:     Michael Forney <forney@...gle.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nick Terrell <terrelln@...com>, Ingo Molnar <mingo@...nel.org>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Kees Cook <keescook@...omium.org>,
        linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org
Cc:     "Alex Xu (Hello71)" <alex_y_xu@...oo.ca>
Subject: [PATCH 2/2] kbuild: pass --stream-size --no-content-size to zstd

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@...oo.ca>
---
 scripts/Makefile.lib | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index ca901814986a..13d756fbcdc7 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -468,10 +468,10 @@ quiet_cmd_xzmisc = XZMISC  $@
 # be used because it would require zstd to allocate a 128 MB buffer.
 
 quiet_cmd_zstd = ZSTD    $@
-      cmd_zstd = { cat $(real-prereqs) | $(ZSTD) -19; $(size_append); } > $@
+      cmd_zstd = { cat $(real-prereqs) | $(ZSTD) --stream-size=$(total_size) --no-content-size -19; $(size_append); } > $@
 
 quiet_cmd_zstd22 = ZSTD22  $@
-      cmd_zstd22 = { cat $(real-prereqs) | $(ZSTD) -22 --ultra; $(size_append); } > $@
+      cmd_zstd22 = { cat $(real-prereqs) | $(ZSTD) --stream-size=$(total_size) --no-content-size -22 --ultra; $(size_append); } > $@
 
 # ASM offsets
 # ---------------------------------------------------------------------------
-- 
2.34.0