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Date:   Wed, 16 Dec 2020 22:07:38 +0000
From:   Nick Terrell <>
To:     David Sterba <>
CC:     Herbert Xu <>,
        Eric Biggers <>,
        Nick Terrell <>,
        Christoph Hellwig <>,
        Yann Collet <>,
        "" <>,
        Petr Malat <>, "Chris Mason" <>,
        "" <>,
        Kernel Team <>,
        Michał Mirosław <>,
        Niket Agarwal <>,
        Btrfs BTRFS <>,
        Johannes Weiner <>
Subject: Re: [f2fs-dev] [PATCH v7 0/3] Update to zstd-1.4.6

> On Dec 16, 2020, at 10:50 AM, David Sterba <> wrote:
> On Wed, Dec 16, 2020 at 11:58:07AM +1100, Herbert Xu wrote:
>> On Wed, Dec 16, 2020 at 12:48:51AM +0000, Nick Terrell wrote:
>>> Thanks for the advice! The first zstd patches went through Herbert’s tree, which is
>>> why I’ve sent them this way.
>> Sorry, but I'm not touch these patches as Christoph's objections
>> don't seem to have been addressed.
> I have objections to the current patchset as well, the build bot has
> found that some of the function frames are overly large (up to 3800
> bytes) [1],

Sorry I missed your reply David, it didn’t make it to my inbox.

Compiled with x86-64, arm, and aarch64 that function does not trigger any
-Wframe-larger-than= warnings during the kernel build. It seems like the
compiler backend for the parisc architecture (the architecture that the build
bot used) is doing a particularly bad job at optimizing this function, because
there is nothing in there that should be using that much stack space.

I have a test in upstream zstd that measures the stack high water mark for
all usage of zstd compression currently in-use the kernel. It says that zstd
uses 2KB of stack space in total on x86-64. I used this test to remove 1KB of
stack usage from upstream zstd. But, this is still 400 bytes more than the
current version of zstd in the kernel. I will look into squeezing out those last
400 bytes of stack usage.

> besides the original complaint that the patch 3/3 is 1.5MiB.
> [1]

It is very large. If it helps, in the commit message I’ve provided this link [0],
which provides the diff between upstream zstd as-is and the imported zstd,
which has been modified by the automated tooling to work in the kernel.



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