> On Dec 5, 2021, at 2:52 PM, Masahiro Yamada <masahiroy@xxxxxxxxxx> wrote: > > On Thu, Nov 25, 2021 at 12:30 AM Alex Xu (Hello71) <alex_y_xu@xxxxxxxx> 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@xxxxxxxx> > > > > > The reason why we need this workaround is just because we do > "cat and compress". zstd must allocate a huge memory beforehand > since it cannot predict how long the stream it will receive. > > If zstd is given with a file name, it can fstat it to know its file size > and allocate the minimal amount of memory. > > > This is my test. > I used 'ulimit' to set the upper limit of the memory the zstd can use. > > > [test steps] > > # Create a 1kB file > $ truncate --size=1k dummy > > # Set the memory size limit to 10MB > $ ulimit -S -v 10240 > > # Pass the file as a argument; success > $ zstd -19 -o dummy.zst dummy > dummy : 2.15% ( 1024 => 22 bytes, dummy.zst) > > # cat and zstd; fail > $ cat dummy | zstd -19 > dummy.zst > zstd: error 11 : Allocation error : not enough memory > > # cat and zstd --stream-size; success > $ cat dummy | zstd -19 --stream-size=1024 > dummy.zst > > > > > scripts/Makefile.modinst was written in such a way > that zstd can know the file size by itself. > > cmd_zstd = $(ZSTD) -T0 --rm -f -q $< > > > We cannot rewrite scripts/Makefile.lib in that way because > arch/x86/boot/compress/Makefile concatenates two files before > compression. And this is the only use-case of this feature. > > So, I am seriously considering to revert this commit: > > commit d3dd3b5a29bb9582957451531fed461628dfc834 > Author: H. Peter Anvin <hpa@xxxxxxxxx> > Date: Tue May 5 21:17:15 2009 -0700 > > kbuild: allow compressors (gzip, bzip2, lzma) to take multiple inputs > > > > > With that commit reverted, zstd will take a single input file, > and we can do "zstd -o <output> <input>". > > > So, I will take some time to investigate that approach. This will definitely work from a zstd perspective. All versions of zstd will downsize their memory usage to match the file size. Best, Nick Terrell >> --- >> 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 >> > > > -- > Best Regards > Masahiro Yamada
