linux-kernel - Re: [PATCH v2 05/28] mm: vmscan: refactor move_folios_to

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Message-ID: <hhrgup42tntpjj5vomztn7lztwqveu25n2vcq4h255dnipadrc@gelesqdlk5c6>
Date: Thu, 18 Dec 2025 16:04:48 -0800
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Qi Zheng <qi.zheng@...ux.dev>
Cc: hannes@...xchg.org, hughd@...gle.com, mhocko@...e.com, 
	roman.gushchin@...ux.dev, muchun.song@...ux.dev, david@...nel.org, 
	lorenzo.stoakes@...cle.com, ziy@...dia.com, harry.yoo@...cle.com, imran.f.khan@...cle.com, 
	kamalesh.babulal@...cle.com, axelrasmussen@...gle.com, yuanchu@...gle.com, weixugc@...gle.com, 
	chenridong@...weicloud.com, mkoutny@...e.com, akpm@...ux-foundation.org, 
	hamzamahfooz@...ux.microsoft.com, apais@...ux.microsoft.com, lance.yang@...ux.dev, 
	linux-mm@...ck.org, linux-kernel@...r.kernel.org, cgroups@...r.kernel.org, 
	Muchun Song <songmuchun@...edance.com>, Qi Zheng <zhengqi.arch@...edance.com>
Subject: Re: [PATCH v2 05/28] mm: vmscan: refactor move_folios_to_lru()

On Wed, Dec 17, 2025 at 03:27:29PM +0800, Qi Zheng wrote:
> From: Muchun Song <songmuchun@...edance.com>
> 
> In a subsequent patch, we'll reparent the LRU folios. The folios that are
> moved to the appropriate LRU list can undergo reparenting during the
> move_folios_to_lru() process. Hence, it's incorrect for the caller to hold
> a lruvec lock. Instead, we should utilize the more general interface of
> folio_lruvec_relock_irq() to obtain the correct lruvec lock.
> 
> This patch involves only code refactoring and doesn't introduce any
> functional changes.
> 
> Signed-off-by: Muchun Song <songmuchun@...edance.com>
> Acked-by: Johannes Weiner <hannes@...xchg.org>
> Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
> ---

[...]
> +	spin_lock_irq(&lruvec->lru_lock);
>  	lru_note_cost_unlock_irq(lruvec, file, stat.nr_pageout,
>  					nr_scanned - nr_reclaimed);

I know that this patch is not changing any functionality but it is
undoing the optimization done by the commit 3865301dc58ae ("mm: optimize
lru_note_cost() by adding lru_note_cost_unlock_irq()"). I think it is
fine as a transient state and I haven't checked the final state of the
code after this series but I think we should do something to restore the
optimization after the series.

Anyways, it's a nit and if no one comes to it, I will take a stab at
restoring the optimization.

For now, LGTM.

Acked-by: Shakeel Butt <shakeel.butt@...ux.dev>