From: Michal Hocko <mhocko@suse.com>
To: "Leonardo Brás" <leobras@redhat.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>,
Marcelo Tosatti <mtosatti@redhat.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Shakeel Butt <shakeelb@google.com>,
Muchun Song <muchun.song@linux.dev>,
Andrew Morton <akpm@linux-foundation.org>,
cgroups@vger.kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org,
Frederic Weisbecker <fweisbecker@suse.de>
Subject: Re: [PATCH v2 0/5] Introduce memcg_stock_pcp remote draining
Date: Fri, 27 Jan 2023 10:23:28 +0100 [thread overview]
Message-ID: <Y9OYEAs+FzuiYd+j@dhcp22.suse.cz> (raw)
In-Reply-To: <601fc35a8cc2167e53e45c636fccb2d899fd7c50.camel@redhat.com>
On Fri 27-01-23 05:12:13, Leonardo Brás wrote:
> On Fri, 2023-01-27 at 04:22 -0300, Leonardo Brás wrote:
> > On Fri, 2023-01-27 at 08:11 +0100, Michal Hocko wrote:
> > > [Cc Frederic]
> > >
> > > On Thu 26-01-23 15:12:35, Roman Gushchin wrote:
> > > > On Thu, Jan 26, 2023 at 08:41:34AM +0100, Michal Hocko wrote:
> > > [...]
> > > > > > Essentially each cpu will try to grab the remains of the memory quota
> > > > > > and move it locally. I wonder in such circumstances if we need to disable the pcp-caching
> > > > > > on per-cgroup basis.
> > > > >
> > > > > I think it would be more than sufficient to disable pcp charging on an
> > > > > isolated cpu.
> > > >
> > > > It might have significant performance consequences.
> > >
> > > Is it really significant?
> > >
> > > > I'd rather opt out of stock draining for isolated cpus: it might slightly reduce
> > > > the accuracy of memory limits and slightly increase the memory footprint (all
> > > > those dying memcgs...), but the impact will be limited. Actually it is limited
> > > > by the number of cpus.
> > >
> > > Hmm, OK, I have misunderstood your proposal. Yes, the overal pcp charges
> > > potentially left behind should be small and that shouldn't really be a
> > > concern for memcg oom situations (unless the limit is very small and
> > > workloads on isolated cpus using small hard limits is way beyond my
> > > imagination).
> > >
> > > My first thought was that those charges could be left behind without any
> > > upper bound but in reality sooner or later something should be running
> > > on those cpus and if the memcg is gone the pcp cache would get refilled
> > > and old charges gone.
> > >
> > > So yes, this is actually a better and even simpler solution. All we need
> > > is something like this
> > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > > index ab457f0394ab..13b84bbd70ba 100644
> > > --- a/mm/memcontrol.c
> > > +++ b/mm/memcontrol.c
> > > @@ -2344,6 +2344,9 @@ static void drain_all_stock(struct mem_cgroup *root_memcg)
> > > struct mem_cgroup *memcg;
> > > bool flush = false;
> > >
> > > + if (cpu_is_isolated(cpu))
> > > + continue;
> > > +
> > > rcu_read_lock();
> > > memcg = stock->cached;
> > > if (memcg && stock->nr_pages &&
> > >
> > > There is no such cpu_is_isolated() AFAICS so we would need a help from
> > > NOHZ and cpuisol people to create one for us. Frederic, would such an
> > > abstraction make any sense from your POV?
> >
> >
> > IIUC, 'if (cpu_is_isolated())' would be instead:
> >
> > if (!housekeeping_cpu(smp_processor_id(), HK_TYPE_DOMAIN) ||
> > !housekeeping_cpu(smp_processor_id(), HK_TYPE_WQ)
>
> oh, sorry 's/smp_processor_id()/cpu/' here:
>
> if(!housekeeping_cpu(cpu, HK_TYPE_DOMAIN) || !housekeeping_cpu(cpu, HK_TYPE_WQ))
Or maybe we can get a nice abstract API so that we do not have to really
care about those low level details. I do not really know what those
really mean and hopefully I shouldn't really need to know.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2023-01-27 9:24 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-25 7:34 [PATCH v2 0/5] Introduce memcg_stock_pcp remote draining Leonardo Bras
2023-01-25 7:34 ` [PATCH v2 1/5] mm/memcontrol: Align percpu memcg_stock to cache Leonardo Bras
2023-01-25 7:34 ` [PATCH v2 2/5] mm/memcontrol: Change stock_lock type from local_lock_t to spinlock_t Leonardo Bras
2023-01-25 7:35 ` [PATCH v2 3/5] mm/memcontrol: Reorder memcg_stock_pcp members to avoid holes Leonardo Bras
2023-01-25 7:35 ` [PATCH v2 4/5] mm/memcontrol: Perform all stock drain in current CPU Leonardo Bras
2023-01-25 7:35 ` [PATCH v2 5/5] mm/memcontrol: Remove flags from memcg_stock_pcp Leonardo Bras
2023-01-25 8:33 ` [PATCH v2 0/5] Introduce memcg_stock_pcp remote draining Michal Hocko
2023-01-25 11:06 ` Leonardo Brás
2023-01-25 11:39 ` Michal Hocko
2023-01-25 18:22 ` Marcelo Tosatti
2023-01-25 23:14 ` Roman Gushchin
2023-01-26 7:41 ` Michal Hocko
2023-01-26 18:03 ` Marcelo Tosatti
2023-01-26 19:20 ` Michal Hocko
2023-01-27 0:32 ` Marcelo Tosatti
2023-01-27 6:58 ` Michal Hocko
2023-02-01 18:31 ` Roman Gushchin
2023-01-26 23:12 ` Roman Gushchin
2023-01-27 7:11 ` Michal Hocko
2023-01-27 7:22 ` Leonardo Brás
2023-01-27 8:12 ` Leonardo Brás
2023-01-27 9:23 ` Michal Hocko [this message]
2023-01-27 13:03 ` Frederic Weisbecker
2023-01-27 13:58 ` Michal Hocko
2023-01-27 18:18 ` Roman Gushchin
2023-02-03 15:21 ` Michal Hocko
2023-02-03 19:25 ` Roman Gushchin
2023-02-13 13:36 ` Michal Hocko
2023-01-27 7:14 ` Leonardo Brás
2023-01-27 7:20 ` Michal Hocko
2023-01-27 7:35 ` Leonardo Brás
2023-01-27 9:29 ` Michal Hocko
2023-01-27 19:29 ` Leonardo Brás
2023-01-27 23:50 ` Roman Gushchin
2023-01-26 18:19 ` Marcelo Tosatti
2023-01-27 5:40 ` Leonardo Brás
2023-01-26 7:45 ` Michal Hocko
2023-01-26 18:14 ` Marcelo Tosatti
2023-01-26 19:13 ` Michal Hocko
2023-01-27 6:55 ` Leonardo Brás
2023-01-31 11:35 ` Marcelo Tosatti
2023-02-01 4:36 ` Leonardo Brás
2023-02-01 12:52 ` Michal Hocko
2023-02-01 12:41 ` Michal Hocko
2023-02-04 4:55 ` Leonardo Brás
2023-02-05 19:49 ` Roman Gushchin
2023-02-07 3:18 ` Leonardo Brás
2023-02-08 19:23 ` Roman Gushchin
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