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Date: Tue, 21 Nov 2017 17:22:39 +0100
From: David Sterba <dsterba@suse.cz>
To: Nick Terrell <terrelln@fb.com>
Cc: "linux-btrfs@vger.kernel.org" <linux-btrfs@vger.kernel.org>,
        Martin Steigerwald <martin@lichtvoll.de>,
        Imran Geriskovan <imran.geriskovan@gmail.com>
Subject: Re: Read before you deploy btrfs + zstd
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On Wed, Nov 15, 2017 at 08:09:15PM +0000, Nick Terrell wrote:
> On 11/15/17, 6:41 AM, "David Sterba" <dsterba@suse.cz> wrote:
> > The branch is now in a state that can be tested. Turns out the memory
> > requirements are too much for grub, so the boot fails with "not enough
> > memory". The calculated value
> >
> > ZSTD_BTRFS_MAX_INPUT: 131072
> > ZSTD_DStreamWorkspaceBound with ZSTD_BTRFS_MAX_INPUT: 549424
> >
> > This is not something I could fix easily, we'd probalby need a tuned
> > version of ZSTD for grub constraints. Adding Nick to CC.
> 
> If I understand the grub code correctly, we only need to read, and we have
> the entire input and output buffer in one segment. In that case you can use
> ZSTD_initDCtx(), and ZSTD_decompressDCtx(). ZSTD_DCtxWorkspaceBound() is
> only 155984. See decompress_single() in
> https://patchwork.kernel.org/patch/9997909/ for an example.

Does not help, still ENOMEM.