linux-kernel - Re: [PATCH 1/4] mm, memcontrol: avoid duplicated memcg enable check

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Message-ID: <tvywr2jdciwljtdx3wlyxgw6ocdkfoqt6hmuchhrqyk66lfsr7@gkz2rfl2u4y2>
Date: Wed, 4 Dec 2024 09:05:52 -0800
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Kairui Song <ryncsn@...il.com>
Cc: Yosry Ahmed <yosryahmed@...gle.com>, linux-mm@...ck.org, 
	Andrew Morton <akpm@...ux-foundation.org>, Chris Li <chrisl@...nel.org>, Hugh Dickins <hughd@...gle.com>, 
	"Huang, Ying" <ying.huang@...el.com>, Roman Gushchin <roman.gushchin@...ux.dev>, 
	Johannes Weiner <hannes@...xchg.org>, Barry Song <baohua@...nel.org>, Michal Hocko <mhocko@...nel.org>, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] mm, memcontrol: avoid duplicated memcg enable check

On Tue, Dec 03, 2024 at 04:25:57PM +0800, Kairui Song wrote:
> On Tue, Dec 3, 2024 at 3:11 AM Yosry Ahmed <yosryahmed@...gle.com> wrote:
> >
> > On Mon, Dec 2, 2024 at 10:42 AM Kairui Song <ryncsn@...il.com> wrote:
> > >
> > > From: Kairui Song <kasong@...cent.com>
> > >
> > > mem_cgroup_uncharge_swap() implies a mem_cgroup_disabled() check,
> > > which is already checked by the caller here. Skip it by calling
> > > __mem_cgroup_uncharge_swap() directly.
> > >
> > > Signed-off-by: Kairui Song <kasong@...cent.com>
> > > ---
> > >  mm/memcontrol.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > > index 7b3503d12aaf..d3d1eb506eee 100644
> > > --- a/mm/memcontrol.c
> > > +++ b/mm/memcontrol.c
> > > @@ -4615,7 +4615,7 @@ void mem_cgroup_swapin_uncharge_swap(swp_entry_t entry, unsigned int nr_pages)
> > >                  * let's not wait for it.  The page already received a
> > >                  * memory+swap charge, drop the swap entry duplicate.
> > >                  */
> > > -               mem_cgroup_uncharge_swap(entry, nr_pages);
> > > +               __mem_cgroup_uncharge_swap(entry, nr_pages);
> >
> > Would it be better to instead remove the mem_cgroup_disabled() check
> > here and have a single check in this path?
> 
> Good suggestion, and the kernel test bot just reported
> __mem_cgroup_uncharge_swap is undefined with !CONFIG_SWAP, so better
> to fix it by removing the check instead.
> 

This sounds reasonable.