From: Shakeel Butt <shakeelb@google.com>
To: Yafang Shao <laoar.shao@gmail.com>
Cc: Mel Gorman <mgorman@suse.de>,
Johannes Weiner <hannes@cmpxchg.org>,
Roman Gushchin <guro@fb.com>, Michal Hocko <mhocko@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Linux MM <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm: vmscan: consistent update to pgsteal and pgscan
Date: Fri, 8 May 2020 06:25:14 -0700 [thread overview]
Message-ID: <CALvZod7VujYgU=6XfgjSZnzLqDpbHwEYsp2Xbq9MK7w_z=LphA@mail.gmail.com> (raw)
In-Reply-To: <CALOAHbAHK4b2p0oWXY6oHG+WQzK3+TEa46=dPabhYT8ab=65zA@mail.gmail.com>
On Fri, May 8, 2020 at 3:34 AM Yafang Shao <laoar.shao@gmail.com> wrote:
>
> On Fri, May 8, 2020 at 4:49 AM Shakeel Butt <shakeelb@google.com> wrote:
> >
> > One way to measure the efficiency of memory reclaim is to look at the
> > ratio (pgscan+pfrefill)/pgsteal. However at the moment these stats are
> > not updated consistently at the system level and the ratio of these are
> > not very meaningful. The pgsteal and pgscan are updated for only global
> > reclaim while pgrefill gets updated for global as well as cgroup
> > reclaim.
> >
>
> Hi Shakeel,
>
> We always use pgscan and pgsteal for monitoring the system level
> memory pressure, for example, by using sysstat(sar) or some other
> monitor tools.
Don't you need pgrefill in addition to pgscan and pgsteal to get the
full picture of the reclaim activity?
> But with this change, these two counters include the memcg pressure as
> well. It is not easy to know whether the pgscan and pgsteal are caused
> by system level pressure or only some specific memcgs reaching their
> memory limit.
>
> How about adding cgroup_reclaim() to pgrefill as well ?
>
I am looking for all the reclaim activity on the system. Adding
!cgroup_reclaim to pgrefill will skip the cgroup reclaim activity.
Maybe adding pgsteal_cgroup and pgscan_cgroup would be better.
> > Please note that this difference is only for system level vmstats. The
> > cgroup stats returned by memory.stat are actually consistent. The
> > cgroup's pgsteal contains number of reclaimed pages for global as well
> > as cgroup reclaim. So, one way to get the system level stats is to get
> > these stats from root's memory.stat but root does not expose that
> > interface. Also for !CONFIG_MEMCG machines /proc/vmstat is the only way
> > to get these stats. So, make these stats consistent.
> >
> > Signed-off-by: Shakeel Butt <shakeelb@google.com>
> > ---
> > mm/vmscan.c | 6 ++----
> > 1 file changed, 2 insertions(+), 4 deletions(-)
> >
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index cc555903a332..51f7d1efc912 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -1943,8 +1943,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
> > reclaim_stat->recent_scanned[file] += nr_taken;
> >
> > item = current_is_kswapd() ? PGSCAN_KSWAPD : PGSCAN_DIRECT;
> > - if (!cgroup_reclaim(sc))
> > - __count_vm_events(item, nr_scanned);
> > + __count_vm_events(item, nr_scanned);
> > __count_memcg_events(lruvec_memcg(lruvec), item, nr_scanned);
> > spin_unlock_irq(&pgdat->lru_lock);
> >
> > @@ -1957,8 +1956,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
> > spin_lock_irq(&pgdat->lru_lock);
> >
> > item = current_is_kswapd() ? PGSTEAL_KSWAPD : PGSTEAL_DIRECT;
> > - if (!cgroup_reclaim(sc))
> > - __count_vm_events(item, nr_reclaimed);
> > + __count_vm_events(item, nr_reclaimed);
> > __count_memcg_events(lruvec_memcg(lruvec), item, nr_reclaimed);
> > reclaim_stat->recent_rotated[0] += stat.nr_activate[0];
> > reclaim_stat->recent_rotated[1] += stat.nr_activate[1];
> > --
> > 2.26.2.526.g744177e7f7-goog
> >
> >
>
>
> --
> Thanks
> Yafang
next prev parent reply other threads:[~2020-05-08 13:25 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-07 20:49 [PATCH] mm: vmscan: consistent update to pgsteal and pgscan Shakeel Butt
2020-05-07 22:28 ` Roman Gushchin
2020-05-08 10:34 ` Yafang Shao
2020-05-08 13:25 ` Shakeel Butt [this message]
2020-05-08 13:38 ` Johannes Weiner
2020-05-08 14:05 ` Shakeel Butt
2020-05-09 6:53 ` Yafang Shao
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