linux-kernel - Re: [PATCH] mm: skip lru_note_cost() when scanning only file or anon

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Message-ID: <878qkqslf2.fsf@linux.dev>
Date: Mon, 14 Jul 2025 10:59:45 -0700
From: Roman Gushchin <roman.gushchin@...ux.dev>
To: Hugh Dickins <hughd@...gle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,  Johannes Weiner
 <hannes@...xchg.org>,  Shakeel Butt <shakeel.butt@...ux.dev>,  Lorenzo
 Stoakes <lorenzo.stoakes@...cle.com>,  Michal Hocko <mhocko@...nel.org>,
  David Hildenbrand <david@...hat.com>,  linux-mm@...ck.org,
  linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: skip lru_note_cost() when scanning only file or anon

Hugh Dickins <hughd@...gle.com> writes:

> Roman, I'm expressing no opinion on your patch above, but please may I
> throw the patch below (against 6.16-rc) over the wall to you, to add as a
> 1/2 or 2/2 to yours (as it stands, it does conflict slightly with yours).
>
> My attention needs to be on other things; but five years ago in
> https://lore.kernel.org/linux-mm/alpine.LSU.2.11.2009211440570.5214@eggly.anvils/
> I noted how lru_note_cost() became more costly with per-memcg lru_lock,
> but did nothing about it at the time.  Apparently now is the time.
>
> Thanks,
> Hugh
>
> [PATCH] mm: lru_note_cost_unlock_irq()
>
> Dropping a lock, just to demand it again for an afterthought, cannot be
> good if contended: convert lru_note_cost() to lru_note_cost_unlock_irq().
>
> Signed-off-by: Hugh Dickins <hughd@...gle.com>

Reviewed-by: Roman Gushchin <roman.gushchin@...ux.dev>
Tested-by: Roman Gushchin <roman.gushchin@...ux.dev>

Thanks, Hugh!

Actually your patch helps quite a lot with the lruvec lock contention
in my test, so I think we can stop looking at my change from the
performance point of view.