Message-ID: <sashiko-outbox-201613@kernel.org>
From: sashiko-bot@kernel.org
Subject: Re: [PATCH v2 03/15] zram: lz4hc: reset the dictionary stream once,
 not per page
Reply-To: sashiko-reviews@lists.linux.dev
To: "Michal Wilczynski" <m.wilczynski@samsung.com>, "Nathan Chancellor" <nathan@kernel.org>, "Nick
 Desaulniers" <ndesaulniers@google.com>, "Bill Wendling" <morbo@google.com>, "Justin
 Stitt" <justinstitt@google.com>, "Russell King" <linux@armlinux.org.uk>, "Thomas
 Bogendoerfer" <tsbogend@alpha.franken.de>, "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>, "Helge
 Deller" <deller@gmx.de>, "Heiko Carstens" <hca@linux.ibm.com>, "Vasily
 Gorbik" <gor@linux.ibm.com>, "Alexander Gordeev" <agordeev@linux.ibm.com>, "Christian
 Borntraeger" <borntraeger@linux.ibm.com>, "Sven Schnelle" <svens@linux.ibm.com>, "Thomas
 Gleixner" <tglx@kernel.org>, "Ingo Molnar" <mingo@redhat.com>, "Borislav
 Petkov" <bp@alien8.de>, "Dave Hansen" <dave.hansen@linux.intel.com>, x86@kernel.org, "H.
 Peter Anvin" <hpa@zytor.com>, "Minchan Kim" <minchan@kernel.org>, "Sergey
 Senozhatsky" <senozhatsky@chromium.org>, "Jens Axboe" <axboe@kernel.dk>, "Andrew
 Morton" <akpm@linux-foundation.org>
Cc: linux-s390@vger.kernel.org, "Yann Collet" <yann.collet.73@gmail.com>, "Nick
 Terrell" <terrelln@meta.com>, "Gao Xiang" <xiang@kernel.org>, "Chao Yu" <chao@kernel.org>, "Jaegeuk
 Kim" <jaegeuk@kernel.org>, "Eric Biggers" <ebiggers@kernel.org>, "Herbert
 Xu" <herbert@gondor.apana.org.au>, "David Laight" <david.laight.linux@gmail.com>, Sungguk <sungguk.na@samsung.com>, "Jaehoon
 Chung" <jh80.chung@samsung.com>, "Marek Szyprowski" <m.szyprowski@samsung.com>, linux-crypto@vger.kernel.org
In-Reply-To: <20261106-lz4-vendor-upstream-v2-3-ee04c3f0d7dc@samsung.com>
References: <20261106-lz4-vendor-upstream-v2-0-ee04c3f0d7dc@samsung.com>
 <CGME20261106144252eucas1p272c9e37d66ad385db070f941879aecb1@eucas1p2.samsung.com>
 <20261106-lz4-vendor-upstream-v2-3-ee04c3f0d7dc@samsung.com>
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Date: Fri, 06 Nov 2026 14:49:28 +0000
Precedence: list

Thank you for your contribution! Sashiko AI review found no new issues
in this patch, but noticed 1 related pre-existing issue it does not
introduce:
- [Medium] zram: high-order memory allocation using kzalloc in
  lz4hc_create() [1]
--

commit 2f51683dc7418bdcd0730283cb7003d8754fcd5f
Author: Michal Wilczynski <m.wilczynski@samsung.com>

zram: lz4hc: reset the dictionary stream once, not per page

This commit moves the LZ4_resetStreamHC() call for dictionary-backed
streams from lz4hc_compress() to lz4hc_create() so that the stream state is
only reset once at creation time rather than on every compressed page.

> diff --git a/drivers/block/zram/backend_lz4hc.c b/drivers/block/zram/back=
end_lz4hc.c
> index d8aa01bb258fe..06286c805cf7c 100644
> --- a/drivers/block/zram/backend_lz4hc.c
> +++ b/drivers/block/zram/backend_lz4hc.c
> @@ -72,6 +72,7 @@ static int lz4hc_create(struct zcomp_params *params, st=
ruct zcomp_ctx *ctx)
>  		zctx->cstrm =3D kzalloc_obj(*zctx->cstrm);
>  		if (!zctx->cstrm)
>  			goto error;
> +		LZ4_resetStreamHC(zctx->cstrm, params->level);
>  	}

[Severity: Medium]
This problem wasn't introduced by this patch, but should zctx->cstrm be
allocated with vmalloc() or kvzalloc() instead of kzalloc_obj() [1]?

LZ4_streamHC_t is 262,192 bytes (LZ4_STREAMHCSIZE), so kzalloc_obj()
requests an order-7 physically contiguous allocation.  Unlike the
non-dictionary path right above, which uses vmalloc(LZ4HC_MEM_COMPRESS),
this allocation can easily fail under normal memory fragmentation during
zram initialization or CPU hotplug.

[1] https://sashiko.dev/#/bug/linux-78ebc045-5e81-4f0b-985e-99483d454b25

--=20
Sashiko AI review =C2=B7 https://sashiko.dev/#/patchset/20261106-lz4-vendor=
-upstream-v2-0-ee04c3f0d7dc@samsung.com?part=3D3