linux-kernel - Re: [PATCH] mm: zswap: Use SG list decompression APIs from zsmalloc

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Message-ID: <uhugzqn3k46hchtk4srsa3uoml4ach5qpl4xm5xqdq6egesvq4@7i7phlkyzjgf>
Date: Wed, 21 Jan 2026 12:49:47 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Yosry Ahmed <yosry.ahmed@...ux.dev>, 
	Herbert Xu <herbert@...dor.apana.org.au>
Cc: Andrew Morton <akpm@...ux-foundation.org>, 
	Johannes Weiner <hannes@...xchg.org>, Nhat Pham <nphamcs@...il.com>, 
	Chengming Zhou <chengming.zhou@...ux.dev>, Sergey Senozhatsky <senozhatsky@...omium.org>, 
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: zswap: Use SG list decompression APIs from zsmalloc

On (26/01/21 01:36), Yosry Ahmed wrote:
> Use the new zs_obj_read_sg_*() APIs in zswap_decompress(), instead of
> zs_obj_read_*() APIs returning a linear address. The SG list is passed
> directly to the crypto API, simplifying the logic and dropping the
> workaround that copies highmem addresses to a buffer. The crypto API
> should internally linearize the SG list if needed.
> 
> This avoids the memcpy() in zsmalloc for objects spanning multiple
> pages, although an equivalent operation will be done internally by
> acomp/scomp. However, in the future compression algorithms could support
> handling discontiguous SG lists, completely eliminating the copying for
> spanning objects.

LGTM.

Once the API lands I think we'll be quite interested in discontiguous
SG lists support in lzo-rle/lzo and lz4 (most commonly used primary
S/W compressors in zram).