From: Johannes Weiner <hannes@cmpxchg.org>
To: Dave Chinner <david@fromorbit.com>
Cc: Yang Shi <shy828301@gmail.com>,
guro@fb.com, ktkhai@virtuozzo.com, shakeelb@google.com,
mhocko@suse.com, akpm@linux-foundation.org, linux-mm@kvack.org,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [v2 PATCH 5/9] mm: memcontrol: add per memcg shrinker nr_deferred
Date: Tue, 15 Dec 2020 15:45:16 +0100 [thread overview]
Message-ID: <20201215144516.GE379720@cmpxchg.org> (raw)
In-Reply-To: <20201215022233.GL3913616@dread.disaster.area>
On Tue, Dec 15, 2020 at 01:22:33PM +1100, Dave Chinner wrote:
> On Mon, Dec 14, 2020 at 02:37:18PM -0800, Yang Shi wrote:
> > Currently the number of deferred objects are per shrinker, but some slabs, for example,
> > vfs inode/dentry cache are per memcg, this would result in poor isolation among memcgs.
> >
> > The deferred objects typically are generated by __GFP_NOFS allocations, one memcg with
> > excessive __GFP_NOFS allocations may blow up deferred objects, then other innocent memcgs
> > may suffer from over shrink, excessive reclaim latency, etc.
> >
> > For example, two workloads run in memcgA and memcgB respectively, workload in B is vfs
> > heavy workload. Workload in A generates excessive deferred objects, then B's vfs cache
> > might be hit heavily (drop half of caches) by B's limit reclaim or global reclaim.
> >
> > We observed this hit in our production environment which was running vfs heavy workload
> > shown as the below tracing log:
> >
> > <...>-409454 [016] .... 28286961.747146: mm_shrink_slab_start: super_cache_scan+0x0/0x1a0 ffff9a83046f3458:
> > nid: 1 objects to shrink 3641681686040 gfp_flags GFP_HIGHUSER_MOVABLE|__GFP_ZERO pgs_scanned 1 lru_pgs 15721
> > cache items 246404277 delta 31345 total_scan 123202138
> > <...>-409454 [022] .... 28287105.928018: mm_shrink_slab_end: super_cache_scan+0x0/0x1a0 ffff9a83046f3458:
> > nid: 1 unused scan count 3641681686040 new scan count 3641798379189 total_scan 602
> > last shrinker return val 123186855
> >
> > The vfs cache and page cache ration was 10:1 on this machine, and half of caches were dropped.
> > This also resulted in significant amount of page caches were dropped due to inodes eviction.
> >
> > Make nr_deferred per memcg for memcg aware shrinkers would solve the unfairness and bring
> > better isolation.
> >
> > When memcg is not enabled (!CONFIG_MEMCG or memcg disabled), the shrinker's nr_deferred
> > would be used. And non memcg aware shrinkers use shrinker's nr_deferred all the time.
> >
> > Signed-off-by: Yang Shi <shy828301@gmail.com>
> > ---
> > include/linux/memcontrol.h | 9 +++
> > mm/memcontrol.c | 110 ++++++++++++++++++++++++++++++++++++-
> > mm/vmscan.c | 4 ++
> > 3 files changed, 120 insertions(+), 3 deletions(-)
> >
> > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> > index 922a7f600465..1b343b268359 100644
> > --- a/include/linux/memcontrol.h
> > +++ b/include/linux/memcontrol.h
> > @@ -92,6 +92,13 @@ struct lruvec_stat {
> > long count[NR_VM_NODE_STAT_ITEMS];
> > };
> >
> > +
> > +/* Shrinker::id indexed nr_deferred of memcg-aware shrinkers. */
> > +struct memcg_shrinker_deferred {
> > + struct rcu_head rcu;
> > + atomic_long_t nr_deferred[];
> > +};
>
> So you're effectively copy and pasting the memcg_shrinker_map
> infrastructure and doubling the number of allocations/frees required
> to set up/tear down a memcg? Why not add it to the struct
> memcg_shrinker_map like this:
>
> struct memcg_shrinker_map {
> struct rcu_head rcu;
> unsigned long *map;
> atomic_long_t *nr_deferred;
> };
>
> And when you dynamically allocate the structure, set the map and
> nr_deferred pointers to the correct offset in the allocated range.
>
> Then this patch is really only changes to the size of the chunk
> being allocated, setting up the pointers and copying the relevant
> data from the old to new.
Fully agreed.
In the longer-term, it may be nice to further expand this and make
this the generalized intersection between cgroup, node and shrinkers.
There is large overlap with list_lru e.g. - with data of identical
scope and lifetime, but duplicative callbacks and management. If we
folded list_lru_memcg into the above data structure, we could also
generalize and reuse the existing callbacks.
next prev parent reply other threads:[~2020-12-15 14:57 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-14 22:37 [RFC v2 PATCH 0/9] Make shrinker's nr_deferred memcg aware Yang Shi
2020-12-14 22:37 ` [v2 PATCH 1/9] mm: vmscan: use nid from shrink_control for tracepoint Yang Shi
2020-12-14 22:37 ` [v2 PATCH 2/9] mm: memcontrol: use shrinker_rwsem to protect shrinker_maps allocation Yang Shi
2020-12-15 2:09 ` Dave Chinner
2020-12-15 13:53 ` Johannes Weiner
2020-12-15 21:59 ` Dave Chinner
2020-12-16 13:17 ` Kirill Tkhai
2020-12-16 19:12 ` Johannes Weiner
2020-12-16 21:56 ` Yang Shi
2020-12-16 19:39 ` Roman Gushchin
2020-12-15 14:07 ` Johannes Weiner
2020-12-15 20:32 ` Yang Shi
2020-12-14 22:37 ` [v2 PATCH 3/9] mm: vmscan: guarantee shrinker_slab_memcg() sees valid shrinker_maps for online memcg Yang Shi
2020-12-15 2:04 ` Dave Chinner
2020-12-15 12:38 ` Johannes Weiner
2020-12-15 12:58 ` Kirill Tkhai
2020-12-15 16:45 ` Johannes Weiner
2020-12-15 17:14 ` Johannes Weiner
2020-12-15 20:31 ` Yang Shi
2020-12-28 20:03 ` Yang Shi
2020-12-14 22:37 ` [v2 PATCH 4/9] mm: vmscan: use a new flag to indicate shrinker is registered Yang Shi
2020-12-14 22:37 ` [v2 PATCH 5/9] mm: memcontrol: add per memcg shrinker nr_deferred Yang Shi
2020-12-15 2:22 ` Dave Chinner
2020-12-15 14:45 ` Johannes Weiner [this message]
2020-12-15 21:57 ` Yang Shi
2020-12-14 22:37 ` [v2 PATCH 6/9] mm: vmscan: use per memcg nr_deferred of shrinker Yang Shi
2020-12-15 2:46 ` Dave Chinner
2020-12-15 22:27 ` Yang Shi
2020-12-15 23:48 ` Dave Chinner
2020-12-14 22:37 ` [v2 PATCH 7/9] mm: vmscan: don't need allocate shrinker->nr_deferred for memcg aware shrinkers Yang Shi
2020-12-15 3:05 ` Dave Chinner
2020-12-15 23:07 ` Yang Shi
2020-12-18 0:56 ` Yang Shi
2020-12-18 1:09 ` Dave Chinner
2020-12-14 22:37 ` [v2 PATCH 8/9] mm: memcontrol: reparent nr_deferred when memcg offline Yang Shi
2020-12-15 3:07 ` Dave Chinner
2020-12-15 23:10 ` Yang Shi
2020-12-14 22:37 ` [v2 PATCH 9/9] mm: vmscan: shrink deferred objects proportional to priority Yang Shi
2020-12-15 3:23 ` Dave Chinner
2020-12-15 23:59 ` Yang Shi
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