From: Michal Hocko <mhocko@kernel.org>
To: Waiman Long <longman@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Mel Gorman <mgorman@suse.de>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
linux-api@vger.kernel.org, Johannes Weiner <hannes@cmpxchg.org>,
Roman Gushchin <guro@fb.com>, Vlastimil Babka <vbabka@suse.cz>,
Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
Jann Horn <jannh@google.com>, Song Liu <songliubraving@fb.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Rafael Aquini <aquini@redhat.com>
Subject: Re: [PATCH 1/2] mm, vmstat: Release zone lock more frequently when reading /proc/pagetypeinfo
Date: Wed, 23 Oct 2019 22:02:56 +0200 [thread overview]
Message-ID: <20191023200256.GP17610@dhcp22.suse.cz> (raw)
In-Reply-To: <58a9adaf-9a1c-398b-dce1-cb30997807c1@redhat.com>
On Wed 23-10-19 14:14:14, Waiman Long wrote:
> On 10/23/19 2:01 PM, Michal Hocko wrote:
> > On Wed 23-10-19 13:34:22, Waiman Long wrote:
> >> With a threshold of 100000, it is still possible that the zone lock
> >> will be held for a very long time in the worst case scenario where all
> >> the counts are just below the threshold. With up to 6 migration types
> >> and 11 orders, it means up to 6.6 millions.
> >>
> >> Track the total number of list iterations done since the acquisition
> >> of the zone lock and release it whenever 100000 iterations or more have
> >> been completed. This will cap the lock hold time to no more than 200,000
> >> list iterations.
> >>
> >> Signed-off-by: Waiman Long <longman@redhat.com>
> >> ---
> >> mm/vmstat.c | 18 ++++++++++++++----
> >> 1 file changed, 14 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/mm/vmstat.c b/mm/vmstat.c
> >> index 57ba091e5460..c5b82fdf54af 100644
> >> --- a/mm/vmstat.c
> >> +++ b/mm/vmstat.c
> >> @@ -1373,6 +1373,7 @@ static void pagetypeinfo_showfree_print(struct seq_file *m,
> >> pg_data_t *pgdat, struct zone *zone)
> >> {
> >> int order, mtype;
> >> + unsigned long iteration_count = 0;
> >>
> >> for (mtype = 0; mtype < MIGRATE_TYPES; mtype++) {
> >> seq_printf(m, "Node %4d, zone %8s, type %12s ",
> >> @@ -1397,15 +1398,24 @@ static void pagetypeinfo_showfree_print(struct seq_file *m,
> >> * of pages in this order should be more than
> >> * sufficient
> >> */
> >> - if (++freecount >= 100000) {
> >> + if (++freecount > 100000) {
> >> overflow = true;
> >> - spin_unlock_irq(&zone->lock);
> >> - cond_resched();
> >> - spin_lock_irq(&zone->lock);
> >> + freecount--;
> >> break;
> >> }
> >> }
> >> seq_printf(m, "%s%6lu ", overflow ? ">" : "", freecount);
> >> + /*
> >> + * Take a break and release the zone lock when
> >> + * 100000 or more entries have been iterated.
> >> + */
> >> + iteration_count += freecount;
> >> + if (iteration_count >= 100000) {
> >> + iteration_count = 0;
> >> + spin_unlock_irq(&zone->lock);
> >> + cond_resched();
> >> + spin_lock_irq(&zone->lock);
> >> + }
> > Aren't you overengineering this a bit? If you are still worried then we
> > can simply cond_resched for each order
> > diff --git a/mm/vmstat.c b/mm/vmstat.c
> > index c156ce24a322..ddb89f4e0486 100644
> > --- a/mm/vmstat.c
> > +++ b/mm/vmstat.c
> > @@ -1399,13 +1399,13 @@ static void pagetypeinfo_showfree_print(struct seq_file *m,
> > */
> > if (++freecount >= 100000) {
> > overflow = true;
> > - spin_unlock_irq(&zone->lock);
> > - cond_resched();
> > - spin_lock_irq(&zone->lock);
> > break;
> > }
> > }
> > seq_printf(m, "%s%6lu ", overflow ? ">" : "", freecount);
> > + spin_unlock_irq(&zone->lock);
> > + cond_resched();
> > + spin_lock_irq(&zone->lock);
> > }
> > seq_putc(m, '\n');
> > }
> >
> > I do not have a strong opinion here but I can fold this into my patch 2.
>
> If the free list is empty or is very short, there is probably no need to
> release and reacquire the lock. How about adding a check for a lower
> bound like:
Again, does it really make any sense to micro optimize something like
this. It is a debugging tool. I would rather go simple.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2019-10-23 20:03 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-22 16:21 [PATCH] mm/vmstat: Reduce zone lock hold time when reading /proc/pagetypeinfo Waiman Long
2019-10-22 16:57 ` Michal Hocko
2019-10-22 18:00 ` Waiman Long
2019-10-22 18:40 ` Waiman Long
2019-10-23 0:52 ` David Rientjes
2019-10-23 8:31 ` Mel Gorman
2019-10-23 9:04 ` Michal Hocko
2019-10-23 9:56 ` Mel Gorman
2019-10-23 10:27 ` [RFC PATCH 0/2] " Michal Hocko
2019-10-23 10:27 ` [RFC PATCH 1/2] mm, vmstat: hide /proc/pagetypeinfo from normal users Michal Hocko
2019-10-23 13:13 ` Mel Gorman
2019-10-23 13:27 ` Vlastimil Babka
2019-10-23 14:52 ` Waiman Long
2019-10-23 15:10 ` Rafael Aquini
2019-10-23 16:15 ` Vlastimil Babka
2019-10-24 19:01 ` David Rientjes
2019-10-23 10:27 ` [RFC PATCH 2/2] mm, vmstat: reduce zone->lock holding time by /proc/pagetypeinfo Michal Hocko
2019-10-23 13:15 ` Mel Gorman
2019-10-23 13:32 ` Vlastimil Babka
2019-10-23 13:37 ` Michal Hocko
2019-10-23 13:48 ` Vlastimil Babka
2019-10-23 14:31 ` Michal Hocko
2019-10-23 16:20 ` Vlastimil Babka
2019-10-23 13:46 ` Rafael Aquini
2019-10-23 14:56 ` Waiman Long
2019-10-23 15:21 ` Waiman Long
2019-10-23 16:10 ` Michal Hocko
2019-10-23 16:17 ` Waiman Long
2019-10-23 16:21 ` Waiman Long
2019-10-23 16:15 ` Vlastimil Babka
2019-10-23 16:41 ` Michal Hocko
2019-10-23 16:47 ` Waiman Long
2019-10-23 17:34 ` [PATCH 1/2] mm, vmstat: Release zone lock more frequently when reading /proc/pagetypeinfo Waiman Long
2019-10-23 18:01 ` Michal Hocko
2019-10-23 18:14 ` Waiman Long
2019-10-23 20:02 ` Michal Hocko [this message]
2019-10-23 17:34 ` [PATCH 2/2] mm, vmstat: List total free blocks for each order in /proc/pagetypeinfo Waiman Long
2019-10-23 18:02 ` Michal Hocko
2019-10-23 18:07 ` Waiman Long
2019-10-24 8:20 ` [RFC PATCH 0/2] mm/vmstat: Reduce zone lock hold time when reading /proc/pagetypeinfo Michal Hocko
2019-10-24 16:16 ` Waiman Long
2019-10-23 12:42 ` [PATCH] " Qian Cai
2019-10-23 13:25 ` Vlastimil Babka
2019-10-22 21:59 ` Andrew Morton
2019-10-23 6:15 ` Michal Hocko
2019-10-23 14:30 ` Waiman Long
2019-10-23 14:48 ` Qian Cai
2019-10-23 15:01 ` Waiman Long
2019-10-23 15:05 ` Qian Cai
2019-10-23 22:30 ` Andrew Morton
2019-10-24 5:33 ` Qian Cai
2019-10-24 7:42 ` Michal Hocko
2019-10-24 11:11 ` Qian Cai
2019-10-24 13:38 ` Michal Hocko
2019-10-24 14:55 ` Qian Cai
2019-10-24 3:33 ` Feng Tang
2019-10-24 4:34 ` Qian Cai
2019-10-24 5:34 ` Feng Tang
2019-10-24 10:51 ` Qian Cai
2019-10-25 1:38 ` Feng Tang
2019-10-23 15:03 ` Rafael Aquini
2019-10-23 15:51 ` Qian Cai
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