linux-kernel - Re: [PATCH] mm: vmscan: protect shrinker idr replace with CONFIG

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Date:   Thu, 5 Dec 2019 10:43:41 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Kirill Tkhai <ktkhai@...tuozzo.com>
Cc:     Yang Shi <yang.shi@...ux.alibaba.com>, hannes@...xchg.org,
        shakeelb@...gle.com, guro@...com, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: vmscan: protect shrinker idr replace with
 CONFIG_MEMCG

On Thu 05-12-19 11:23:28, Kirill Tkhai wrote:
> On 04.12.2019 22:16, Yang Shi wrote:
> > Since commit 0a432dcbeb32edcd211a5d8f7847d0da7642a8b4 ("mm: shrinker:
> > make shrinker not depend on memcg kmem"), shrinkers' idr is protected by
> > CONFIG_MEMCG instead of CONFIG_MEMCG_KMEM, so it makes no sense to
> > protect shrinker idr replace with CONFIG_MEMCG_KMEM.
> > 
> > Cc: Kirill Tkhai <ktkhai@...tuozzo.com>
> > Cc: Johannes Weiner <hannes@...xchg.org>
> > Cc: Michal Hocko <mhocko@...e.com>
> > Cc: Shakeel Butt <shakeelb@...gle.com>
> > Cc: Roman Gushchin <guro@...com>
> > Signed-off-by: Yang Shi <yang.shi@...ux.alibaba.com>
> 
> It looks like that in CONFIG_SLOB case we do not even call some shrinkers
> for subordinate mem cgroups (i.e., we don't call deferred_split_shrinker),
> since they never become completely registered.
> 
> Fixes: 0a432dcbeb32edcd211a5d8f7847d0da7642a8b4 ("mm: shrinker: make shrinker not depend on memcg kmem")

I am confused. Why the Fixes tag? Nothing should be really broken with
KMEM config guard right?

This is a mere clean up AFAICS.

> Reviewed-by: Kirill Tkhai <ktkhai@...tuozzo.com>
> 
> > ---
> >  mm/vmscan.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index ee4eecc..e7f10c4 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -422,7 +422,7 @@ void register_shrinker_prepared(struct shrinker *shrinker)
> >  {
> >  	down_write(&shrinker_rwsem);
> >  	list_add_tail(&shrinker->list, &shrinker_list);
> > -#ifdef CONFIG_MEMCG_KMEM
> > +#ifdef CONFIG_MEMCG
> >  	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> >  		idr_replace(&shrinker_idr, shrinker, shrinker->id);
> >  #endif
> > 

-- 
Michal Hocko
SUSE Labs