From: Michal Hocko <mhocko@kernel.org>
To: Balbir Singh <bsingharora@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Mel Gorman <mgorman@suse.de>,
Johannes Weiner <hannes@cmpxchg.org>,
Vlastimil Babka <vbabka@suse.cz>, linux-mm <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
Boris Zhmurov <bb@kernelpanic.ru>,
"Christopher S. Aker" <caker@theshore.net>,
Donald Buczek <buczek@molgen.mpg.de>,
Paul Menzel <pmenzel@molgen.mpg.de>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: Re: [PATCH] mm, vmscan: add cond_resched into shrink_node_memcg
Date: Mon, 5 Dec 2016 13:49:55 +0100 [thread overview]
Message-ID: <20161205124955.GG30758@dhcp22.suse.cz> (raw)
In-Reply-To: <CAKTCnz=K8QG69tKB8yStiZypBzcvnE=wW+25xuo9f_HZNzPtDg@mail.gmail.com>
[CC Paul - sorry I've tried to save you from more emails...]
On Mon 05-12-16 23:44:27, Balbir Singh wrote:
> >
> > Hi,
> > there were multiple reportes of the similar RCU stalls. Only Boris has
> > confirmed that this patch helps in his workload. Others might see a
> > slightly different issue and that should be investigated if it is the
> > case. As pointed out by Paul [1] cond_resched might be not sufficient
> > to silence RCU stalls because that would require a real scheduling.
> > This is a separate problem, though, and Paul is working with Peter [2]
> > to resolve it.
> >
> > Anyway, I believe that this patch should be a good start because it
> > really seems that nr_taken=0 during the LRU isolation can be triggered
> > in the real life. All reporters are agreeing to start seeing this issue
> > when moving on to 4.8 kernel which might be just a coincidence or a
> > different behavior of some subsystem. Well, MM has moved from zone to
> > node reclaim but I couldn't have found any direct relation to that
> > change.
> >
> > [1] http://lkml.kernel.org/r/20161130142955.GS3924@linux.vnet.ibm.com
> > [2] http://lkml.kernel.org/r/20161201124024.GB3924@linux.vnet.ibm.com
> >
> > mm/vmscan.c | 2 ++
> > 1 file changed, 2 insertions(+)
> >
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index c05f00042430..c4abf08861d2 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -2362,6 +2362,8 @@ static void shrink_node_memcg(struct pglist_data *pgdat, struct mem_cgroup *memc
> > }
> > }
> >
> > + cond_resched();
> > +
>
> I see a cond_resched_rcu_qs() as a part of linux next inside the while
> (nr[..]) loop.
This is a left over from Paul's initial attempt to fix this issue. I
expect him to drop his patch from his tree. He has considered it
experimental anyway.
> Do we need this as well?
Paul is working with Peter to make cond_resched general and cover RCU
stalls even when cond_resched doesn't schedule because there is no
runnable task.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2016-12-05 12:50 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-02 9:58 [PATCH] mm, vmscan: add cond_resched into shrink_node_memcg Michal Hocko
2016-12-05 12:44 ` Balbir Singh
2016-12-05 12:49 ` Michal Hocko [this message]
2016-12-05 16:16 ` Paul E. McKenney
2016-12-09 10:13 ` Donald Buczek
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