linux-kernel - Re: [PATCH v1 5/6] memcg-v1: no need for memcg locking for MGLRU

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Message-ID: <zyg74lpsxu7gvnsjjrcrbejfophvas6ibfi6cpqsj6hewgongo@x6hlpemfz6ej>
Date: Fri, 25 Oct 2024 23:20:52 -0700
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Yu Zhao <yuzhao@...gle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, 
	Johannes Weiner <hannes@...xchg.org>, Michal Hocko <mhocko@...nel.org>, 
	Roman Gushchin <roman.gushchin@...ux.dev>, Muchun Song <muchun.song@...ux.dev>, 
	Hugh Dickins <hughd@...gle.com>, Yosry Ahmed <yosryahmed@...gle.com>, linux-mm@...ck.org, 
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
	linux-doc@...r.kernel.org, Meta kernel team <kernel-team@...a.com>
Subject: Re: [PATCH v1 5/6] memcg-v1: no need for memcg locking for MGLRU

On Fri, Oct 25, 2024 at 09:55:38PM GMT, Yu Zhao wrote:
> On Thu, Oct 24, 2024 at 7:23 PM Shakeel Butt <shakeel.butt@...ux.dev> wrote:
> >
> > While updating the generation of the folios, MGLRU requires that the
> > folio's memcg association remains stable. With the charge migration
> > deprecated, there is no need for MGLRU to acquire locks to keep the
> > folio and memcg association stable.
> >
> > Signed-off-by: Shakeel Butt <shakeel.butt@...ux.dev>
> > ---
> >  mm/vmscan.c | 11 -----------
> >  1 file changed, 11 deletions(-)
> >
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index 29c098790b01..fd7171658b63 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -3662,10 +3662,6 @@ static void walk_mm(struct mm_struct *mm, struct lru_gen_mm_walk *walk)
> >                 if (walk->seq != max_seq)
> >                         break;
> 
> Please remove the lingering `struct mem_cgroup *memcg` as well as
> folio_memcg_rcu(). Otherwise it causes both build and lockdep
> warnings.
> 

Thanks for catching this. The unused warning is already fixed by Andrew,
I will fix the folio_memcg_rcu() usage.