linux-kernel - Re: [PATCH 1/4] mm/zswap: remove unnecessary dlen writes for incompressible pages

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Message-ID: <xdsrooh5v7hdkfzr4rmwg6bmg2kd7wediwk7efjexu3ken3wec@so6hlaxqvafh>
Date: Tue, 7 Oct 2025 23:40:21 +0000
From: Yosry Ahmed <yosry.ahmed@...ux.dev>
To: SeongJae Park <sj@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>, 
	Chengming Zhou <chengming.zhou@...ux.dev>, Johannes Weiner <hannes@...xchg.org>, 
	Nhat Pham <nphamcs@...il.com>, kernel-team@...a.com, linux-kernel@...r.kernel.org, 
	linux-mm@...ck.org
Subject: Re: [PATCH 1/4] mm/zswap: remove unnecessary dlen writes for
 incompressible pages

On Fri, Oct 03, 2025 at 01:38:48PM -0700, SeongJae Park wrote:
> Incompressible pages handling logic in zswap_compress() is setting
> 'dlen' as PAGE_SIZE twice.  Once before deciding whether to save the
> content as is, and once again after it is decided to save it as is.
> But the value of 'dlen' is used only if it is decided to save the
> content as is, so the first write is unnecessary.  It is not causing
> real user issues, but making code confusing to read.  Remove the
> unnecessary write operation.
> 
> Signed-off-by: SeongJae Park <sj@...nel.org>

Acked-by: Yosry Ahmed <yosry.ahmed@...ux.dev>

> ---
>  mm/zswap.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/mm/zswap.c b/mm/zswap.c
> index c1af782e54ec..80619c8589a7 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -894,7 +894,6 @@ static bool zswap_compress(struct page *page, struct zswap_entry *entry,
>  	 * to the active LRU list in the case.
>  	 */
>  	if (comp_ret || !dlen || dlen >= PAGE_SIZE) {
> -		dlen = PAGE_SIZE;
>  		if (!mem_cgroup_zswap_writeback_enabled(
>  					folio_memcg(page_folio(page)))) {
>  			comp_ret = comp_ret ? comp_ret : -EINVAL;
> -- 
> 2.39.5