From: Yang Shi <shy828301@gmail.com>
To: Kirill Tkhai <ktkhai@virtuozzo.com>
Cc: Roman Gushchin <guro@fb.com>, Vlastimil Babka <vbabka@suse.cz>,
Shakeel Butt <shakeelb@google.com>,
Dave Chinner <david@fromorbit.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Michal Hocko <mhocko@suse.com>,
Andrew Morton <akpm@linux-foundation.org>,
Linux MM <linux-mm@kvack.org>,
Linux FS-devel Mailing List <linux-fsdevel@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [v6 PATCH 11/11] mm: vmscan: shrink deferred objects proportional to priority
Date: Thu, 4 Feb 2021 09:29:06 -0800 [thread overview]
Message-ID: <CAHbLzkp6du=4rRcy2hxQrWo_2GX9QUcZuAyFqe_hiimDr6axyQ@mail.gmail.com> (raw)
In-Reply-To: <8c11f94a-bd1a-3311-2160-0f2c83994a53@virtuozzo.com>
On Thu, Feb 4, 2021 at 2:23 AM Kirill Tkhai <ktkhai@virtuozzo.com> wrote:
>
> On 03.02.2021 20:20, Yang Shi wrote:
> > The number of deferred objects might get windup to an absurd number, and it
> > results in clamp of slab objects. It is undesirable for sustaining workingset.
> >
> > So shrink deferred objects proportional to priority and cap nr_deferred to twice
> > of cache items.
> >
> > The idea is borrowed fron Dave Chinner's patch:
> > https://lore.kernel.org/linux-xfs/20191031234618.15403-13-david@fromorbit.com/
> >
> > Tested with kernel build and vfs metadata heavy workload in our production
> > environment, no regression is spotted so far.
> >
> > Signed-off-by: Yang Shi <shy828301@gmail.com>
>
> For some time I was away from this do_shrink_slab() magic formulas and recent changes,
> so I hope somebody else, who is being in touch with this, can review.
Yes, I agree it is intimidating. The patch has been tested in our test
and production environment for a couple of months, so far no
regression is spotted. Of course it doesn't mean it will not incur
regression for other workloads. My plan is to leave it stay in -mm
then linux-next for a while for a broader test. The first 10 patches
could go to Linus's tree separately.
>
> > ---
> > mm/vmscan.c | 40 +++++-----------------------------------
> > 1 file changed, 5 insertions(+), 35 deletions(-)
> >
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index 574d920c4cab..d0a86170854b 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -649,7 +649,6 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
> > */
> > nr = count_nr_deferred(shrinker, shrinkctl);
> >
> > - total_scan = nr;
> > if (shrinker->seeks) {
> > delta = freeable >> priority;
> > delta *= 4;
> > @@ -663,37 +662,9 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
> > delta = freeable / 2;
> > }
> >
> > + total_scan = nr >> priority;
> > total_scan += delta;
> > - if (total_scan < 0) {
> > - pr_err("shrink_slab: %pS negative objects to delete nr=%ld\n",
> > - shrinker->scan_objects, total_scan);
> > - total_scan = freeable;
> > - next_deferred = nr;
> > - } else
> > - next_deferred = total_scan;
> > -
> > - /*
> > - * We need to avoid excessive windup on filesystem shrinkers
> > - * due to large numbers of GFP_NOFS allocations causing the
> > - * shrinkers to return -1 all the time. This results in a large
> > - * nr being built up so when a shrink that can do some work
> > - * comes along it empties the entire cache due to nr >>>
> > - * freeable. This is bad for sustaining a working set in
> > - * memory.
> > - *
> > - * Hence only allow the shrinker to scan the entire cache when
> > - * a large delta change is calculated directly.
> > - */
> > - if (delta < freeable / 4)
> > - total_scan = min(total_scan, freeable / 2);
> > -
> > - /*
> > - * Avoid risking looping forever due to too large nr value:
> > - * never try to free more than twice the estimate number of
> > - * freeable entries.
> > - */
> > - if (total_scan > freeable * 2)
> > - total_scan = freeable * 2;
> > + total_scan = min(total_scan, (2 * freeable));
> >
> > trace_mm_shrink_slab_start(shrinker, shrinkctl, nr,
> > freeable, delta, total_scan, priority);
> > @@ -732,10 +703,9 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
> > cond_resched();
> > }
> >
> > - if (next_deferred >= scanned)
> > - next_deferred -= scanned;
> > - else
> > - next_deferred = 0;
> > + next_deferred = max_t(long, (nr - scanned), 0) + total_scan;
> > + next_deferred = min(next_deferred, (2 * freeable));
> > +
> > /*
> > * move the unused scan count back into the shrinker in a
> > * manner that handles concurrent updates.
>
> Thanks
>
>
prev parent reply other threads:[~2021-02-04 17:29 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-03 17:20 [v6 PATCH 0/11] Make shrinker's nr_deferred memcg aware Yang Shi
2021-02-03 17:20 ` [v6 PATCH 01/11] mm: vmscan: use nid from shrink_control for tracepoint Yang Shi
2021-02-04 7:22 ` Kirill Tkhai
2021-02-03 17:20 ` [v6 PATCH 02/11] mm: vmscan: consolidate shrinker_maps handling code Yang Shi
2021-02-04 7:23 ` Kirill Tkhai
2021-02-03 17:20 ` [v6 PATCH 03/11] mm: vmscan: use shrinker_rwsem to protect shrinker_maps allocation Yang Shi
2021-02-04 7:24 ` Kirill Tkhai
2021-02-03 17:20 ` [v6 PATCH 04/11] mm: vmscan: remove memcg_shrinker_map_size Yang Shi
2021-02-04 8:01 ` Kirill Tkhai
2021-02-03 17:20 ` [v6 PATCH 05/11] mm: memcontrol: rename shrinker_map to shrinker_info Yang Shi
2021-02-04 8:03 ` Kirill Tkhai
2021-02-03 17:20 ` [v6 PATCH 06/11] mm: vmscan: use a new flag to indicate shrinker is registered Yang Shi
2021-02-04 8:15 ` Kirill Tkhai
2021-02-03 17:20 ` [v6 PATCH 07/11] mm: vmscan: add per memcg shrinker nr_deferred Yang Shi
2021-02-04 8:30 ` Kirill Tkhai
2021-02-04 17:17 ` Yang Shi
2021-02-05 14:37 ` Kirill Tkhai
2021-02-05 16:49 ` Yang Shi
2021-02-03 17:20 ` [v6 PATCH 08/11] mm: vmscan: use per memcg nr_deferred of shrinker Yang Shi
2021-02-04 8:41 ` Kirill Tkhai
2021-02-04 17:23 ` Yang Shi
2021-02-05 14:41 ` Kirill Tkhai
2021-02-05 16:40 ` Yang Shi
2021-02-05 3:12 ` [mm] [confidence: ] 3510a44e0e: WARNING:suspicious_RCU_usage kernel test robot
2021-02-03 17:20 ` [v6 PATCH 09/11] mm: vmscan: don't need allocate shrinker->nr_deferred for memcg aware shrinkers Yang Shi
2021-02-04 9:29 ` Kirill Tkhai
2021-02-04 10:14 ` Kirill Tkhai
2021-02-04 17:32 ` Yang Shi
2021-02-05 14:44 ` Kirill Tkhai
2021-02-03 17:20 ` [v6 PATCH 10/11] mm: memcontrol: reparent nr_deferred when memcg offline Yang Shi
2021-02-04 10:15 ` Kirill Tkhai
2021-02-03 17:20 ` [v6 PATCH 11/11] mm: vmscan: shrink deferred objects proportional to priority Yang Shi
2021-02-04 10:23 ` Kirill Tkhai
2021-02-04 17:29 ` Yang Shi [this message]
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