From: Roman Gushchin <guro@fb.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: Naresh Kamboju <naresh.kamboju@linaro.org>,
Shakeel Butt <shakeelb@google.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm <linux-mm@kvack.org>,
open list <linux-kernel@vger.kernel.org>,
<lkft-triage@lists.linaro.org>, Chris Down <chris@chrisdown.name>
Subject: Re: BUG: Bad page state in process - page dumped because: page still charged to cgroup
Date: Thu, 2 Jul 2020 10:19:42 -0700 [thread overview]
Message-ID: <20200702171942.GC106423@carbon.dhcp.thefacebook.com> (raw)
In-Reply-To: <20200702171302.GK18446@dhcp22.suse.cz>
On Thu, Jul 02, 2020 at 07:13:02PM +0200, Michal Hocko wrote:
> On Thu 02-07-20 09:37:38, Roman Gushchin wrote:
> > On Thu, Jul 02, 2020 at 06:22:02PM +0200, Michal Hocko wrote:
> > > On Wed 01-07-20 11:45:52, Roman Gushchin wrote:
> > > [...]
> > > > >From c97afecd32c0db5e024be9ba72f43d22974f5bcd Mon Sep 17 00:00:00 2001
> > > > From: Roman Gushchin <guro@fb.com>
> > > > Date: Wed, 1 Jul 2020 11:05:32 -0700
> > > > Subject: [PATCH] mm: kmem: make memcg_kmem_enabled() irreversible
> > > >
> > > > Historically the kernel memory accounting was an opt-in feature, which
> > > > could be enabled for individual cgroups. But now it's not true, and
> > > > it's on by default both on cgroup v1 and cgroup v2. And as long as a
> > > > user has at least one non-root memory cgroup, the kernel memory
> > > > accounting is on. So in most setups it's either always on (if memory
> > > > cgroups are in use and kmem accounting is not disabled), either always
> > > > off (otherwise).
> > > >
> > > > memcg_kmem_enabled() is used in many places to guard the kernel memory
> > > > accounting code. If memcg_kmem_enabled() can reverse from returning
> > > > true to returning false (as now), we can't rely on it on release paths
> > > > and have to check if it was on before.
> > > >
> > > > If we'll make memcg_kmem_enabled() irreversible (always returning true
> > > > after returning it for the first time), it'll make the general logic
> > > > more simple and robust. It also will allow to guard some checks which
> > > > otherwise would stay unguarded.
> > > >
> > > > Signed-off-by: Roman Gushchin <guro@fb.com>
> > > > ---
> > > > mm/memcontrol.c | 6 ++----
> > > > 1 file changed, 2 insertions(+), 4 deletions(-)
> > > >
> > > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > > > index 50ae77f3985e..2d018a51c941 100644
> > > > --- a/mm/memcontrol.c
> > > > +++ b/mm/memcontrol.c
> > > > @@ -3582,7 +3582,8 @@ static int memcg_online_kmem(struct mem_cgroup *memcg)
> > > > objcg->memcg = memcg;
> > > > rcu_assign_pointer(memcg->objcg, objcg);
> > > >
> > > > - static_branch_inc(&memcg_kmem_enabled_key);
> > > > + if (!memcg_kmem_enabled())
> > > > + static_branch_inc(&memcg_kmem_enabled_key);
> > >
> > > Wouldn't be static_branch_enable() more readable?
> >
> > Agree, will change, add reported-by and tested-by tags and resend.
> > Thanks!
>
> Feel free to add
> Acked-by: Michal Hocko <mhocko@suse.com>
Thank you!
>
> > Btw, don't we wanna to change memcg_kmem_enabled() definition
> > from static_branch_unlikely() to static_branch_likely()?
>
> Honestly, I do not know what would be the impact but considering kmem
> is enabled unless explicitly disabled these days then likely sounds more
> logical from reading POV. I do not think that early allocations until
> the first memcg is created is the case to optimize for.
> Worth a separate patch I guess.
Yeah, I doubt there will be any measurable difference, it just strained my eyes.
I prepare a small set of cleanups/cosmetic fixes, will add it to them.
Thanks!
prev parent reply other threads:[~2020-07-02 17:20 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-01 8:18 BUG: Bad page state in process - page dumped because: page still charged to cgroup Naresh Kamboju
2020-07-01 8:29 ` Michal Hocko
2020-07-01 12:31 ` Naresh Kamboju
2020-07-01 18:45 ` Roman Gushchin
2020-07-02 6:19 ` Michal Hocko
2020-07-02 6:52 ` Naresh Kamboju
2020-07-02 15:49 ` Roman Gushchin
2020-07-02 15:55 ` Naresh Kamboju
2020-07-02 15:59 ` Roman Gushchin
2020-07-02 16:02 ` Shakeel Butt
2020-07-02 16:22 ` Michal Hocko
2020-07-02 16:35 ` Vlastimil Babka
2020-07-02 17:07 ` Roman Gushchin
2020-07-02 17:10 ` Michal Hocko
2020-07-02 16:37 ` Roman Gushchin
2020-07-02 17:13 ` Michal Hocko
2020-07-02 17:19 ` Roman Gushchin [this message]
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