linux-kernel - Re: [PATCHv2 1/2] zsmalloc: use actual object size to detect spans

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Message-ID: <CAKEwX=POodPuBkKkQvgt7R7cbjJ1z5CJ=sKLAA5uWsEX7OyrgA@mail.gmail.com>
Date: Wed, 14 Jan 2026 13:17:57 +0900
From: Nhat Pham <nphamcs@...il.com>
To: Sergey Senozhatsky <senozhatsky@...omium.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Yosry Ahmed <yosry.ahmed@...ux.dev>, 
	Minchan Kim <minchan@...nel.org>, Johannes Weiner <hannes@...xchg.org>, 
	Brian Geffon <bgeffon@...gle.com>, linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCHv2 1/2] zsmalloc: use actual object size to detect spans

On Wed, Jan 7, 2026 at 2:24 PM Sergey Senozhatsky
<senozhatsky@...omium.org> wrote:
>
> Using class->size to detect spanning objects is not entirely correct,
> because some size classes can hold a range of object sizes of up to
> class->size bytes in length, due to size-classes merge.  Such classes
> use padding for cases when actually written objects are smaller than
> class->size.  zs_obj_read_begin() can incorrectly hit the slow path
> and perform memcpy of such objects, basically copying padding bytes.
> Instead of class->size zs_obj_read_begin() should use the actual
> compressed object length (both zram and zswap know it) so that it can
> correctly handle situations when a written object is small enough to
> fit into the first physical page.
>
> Signed-off-by: Sergey Senozhatsky <senozhatsky@...omium.org>
> ---
>

LGTM!

Reviewed-by: Nhat Pham <nphamcs@...il.com>