From: Vladimir Davydov <vdavydov.dev@gmail.com>
To: Kirill Tkhai <ktkhai@virtuozzo.com>
Cc: akpm@linux-foundation.org, shakeelb@google.com,
viro@zeniv.linux.org.uk, hannes@cmpxchg.org, mhocko@kernel.org,
tglx@linutronix.de, pombredanne@nexb.com,
stummala@codeaurora.org, gregkh@linuxfoundation.org,
sfr@canb.auug.org.au, guro@fb.com, mka@chromium.org,
penguin-kernel@I-love.SAKURA.ne.jp, chris@chris-wilson.co.uk,
longman@redhat.com, minchan@kernel.org, ying.huang@intel.com,
mgorman@techsingularity.net, jbacik@fb.com, linux@roeck-us.net,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
willy@infradead.org, lirongqing@baidu.com,
aryabinin@virtuozzo.com
Subject: Re: [PATCH v5 13/13] mm: Clear shrinker bit if there are no objects related to memcg
Date: Tue, 15 May 2018 08:59:13 +0300 [thread overview]
Message-ID: <20180515055913.alk3pau43e3jps3y@esperanza> (raw)
In-Reply-To: <152594605549.22949.16491037134168999424.stgit@localhost.localdomain>
On Thu, May 10, 2018 at 12:54:15PM +0300, Kirill Tkhai wrote:
> To avoid further unneed calls of do_shrink_slab()
> for shrinkers, which already do not have any charged
> objects in a memcg, their bits have to be cleared.
>
> This patch introduces a lockless mechanism to do that
> without races without parallel list lru add. After
> do_shrink_slab() returns SHRINK_EMPTY the first time,
> we clear the bit and call it once again. Then we restore
> the bit, if the new return value is different.
>
> Note, that single smp_mb__after_atomic() in shrink_slab_memcg()
> covers two situations:
>
> 1)list_lru_add() shrink_slab_memcg
> list_add_tail() for_each_set_bit() <--- read bit
> do_shrink_slab() <--- missed list update (no barrier)
> <MB> <MB>
> set_bit() do_shrink_slab() <--- seen list update
>
> This situation, when the first do_shrink_slab() sees set bit,
> but it doesn't see list update (i.e., race with the first element
> queueing), is rare. So we don't add <MB> before the first call
> of do_shrink_slab() instead of this to do not slow down generic
> case. Also, it's need the second call as seen in below in (2).
>
> 2)list_lru_add() shrink_slab_memcg()
> list_add_tail() ...
> set_bit() ...
> ... for_each_set_bit()
> do_shrink_slab() do_shrink_slab()
> clear_bit() ...
> ... ...
> list_lru_add() ...
> list_add_tail() clear_bit()
> <MB> <MB>
> set_bit() do_shrink_slab()
>
> The barriers guarantees, the second do_shrink_slab()
> in the right side task sees list update if really
> cleared the bit. This case is drawn in the code comment.
>
> [Results/performance of the patchset]
>
> After the whole patchset applied the below test shows signify
> increase of performance:
>
> $echo 1 > /sys/fs/cgroup/memory/memory.use_hierarchy
> $mkdir /sys/fs/cgroup/memory/ct
> $echo 4000M > /sys/fs/cgroup/memory/ct/memory.kmem.limit_in_bytes
> $for i in `seq 0 4000`; do mkdir /sys/fs/cgroup/memory/ct/$i; echo $$ > /sys/fs/cgroup/memory/ct/$i/cgroup.procs; mkdir -p s/$i; mount -t tmpfs $i s/$i; touch s/$i/file; done
>
> Then, 5 sequential calls of drop caches:
> $time echo 3 > /proc/sys/vm/drop_caches
>
> 1)Before:
> 0.00user 13.78system 0:13.78elapsed 99%CPU
> 0.00user 5.59system 0:05.60elapsed 99%CPU
> 0.00user 5.48system 0:05.48elapsed 99%CPU
> 0.00user 8.35system 0:08.35elapsed 99%CPU
> 0.00user 8.34system 0:08.35elapsed 99%CPU
>
> 2)After
> 0.00user 1.10system 0:01.10elapsed 99%CPU
> 0.00user 0.00system 0:00.01elapsed 64%CPU
> 0.00user 0.01system 0:00.01elapsed 82%CPU
> 0.00user 0.00system 0:00.01elapsed 64%CPU
> 0.00user 0.01system 0:00.01elapsed 82%CPU
>
> The results show the performance increases at least in 548 times.
>
> Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
> ---
> include/linux/memcontrol.h | 2 ++
> mm/vmscan.c | 19 +++++++++++++++++--
> 2 files changed, 19 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 436691a66500..82c0bf2d0579 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -1283,6 +1283,8 @@ static inline void memcg_set_shrinker_bit(struct mem_cgroup *memcg, int nid, int
>
> rcu_read_lock();
> map = MEMCG_SHRINKER_MAP(memcg, nid);
> + /* Pairs with smp mb in shrink_slab() */
> + smp_mb__before_atomic();
> set_bit(nr, map->map);
> rcu_read_unlock();
> }
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 7b0075612d73..189b163bef4a 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -586,8 +586,23 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
> continue;
>
> ret = do_shrink_slab(&sc, shrinker, priority);
> - if (ret == SHRINK_EMPTY)
> - ret = 0;
> + if (ret == SHRINK_EMPTY) {
> + clear_bit(i, map->map);
> + /*
> + * Pairs with mb in memcg_set_shrinker_bit():
> + *
> + * list_lru_add() shrink_slab_memcg()
> + * list_add_tail() clear_bit()
> + * <MB> <MB>
> + * set_bit() do_shrink_slab()
> + */
Please improve the comment so that it isn't just a diagram.
> + smp_mb__after_atomic();
> + ret = do_shrink_slab(&sc, shrinker, priority);
> + if (ret == SHRINK_EMPTY)
> + ret = 0;
> + else
> + memcg_set_shrinker_bit(memcg, nid, i);
> + }
> freed += ret;
>
> if (rwsem_is_contended(&shrinker_rwsem)) {
>
next prev parent reply other threads:[~2018-05-15 5:59 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-10 9:52 [PATCH v5 00/13] Improve shrink_slab() scalability (old complexity was O(n^2), new is O(n)) Kirill Tkhai
2018-05-10 9:52 ` [PATCH v5 01/13] mm: Assign id to every memcg-aware shrinker Kirill Tkhai
2018-05-13 5:15 ` Vladimir Davydov
2018-05-14 9:03 ` Kirill Tkhai
2018-05-15 3:29 ` Vladimir Davydov
2018-05-10 9:52 ` [PATCH v5 02/13] memcg: Move up for_each_mem_cgroup{, _tree} defines Kirill Tkhai
2018-05-10 9:52 ` [PATCH v5 03/13] mm: Assign memcg-aware shrinkers bitmap to memcg Kirill Tkhai
2018-05-13 16:47 ` Vladimir Davydov
2018-05-14 9:34 ` Kirill Tkhai
2018-05-15 3:54 ` Vladimir Davydov
2018-05-10 9:52 ` [PATCH v5 04/13] mm: Refactoring in workingset_init() Kirill Tkhai
2018-05-10 9:52 ` [PATCH v5 05/13] fs: Refactoring in alloc_super() Kirill Tkhai
2018-05-10 9:53 ` [PATCH v5 06/13] fs: Propagate shrinker::id to list_lru Kirill Tkhai
2018-05-13 16:57 ` Vladimir Davydov
2018-05-10 9:53 ` [PATCH v5 07/13] list_lru: Add memcg argument to list_lru_from_kmem() Kirill Tkhai
2018-05-10 9:53 ` [PATCH v5 08/13] list_lru: Pass dst_memcg argument to memcg_drain_list_lru_node() Kirill Tkhai
2018-05-10 9:53 ` [PATCH v5 09/13] list_lru: Pass lru " Kirill Tkhai
2018-05-10 9:53 ` [PATCH v5 10/13] mm: Set bit in memcg shrinker bitmap on first list_lru item apearance Kirill Tkhai
2018-05-15 4:08 ` Vladimir Davydov
2018-05-10 9:53 ` [PATCH v5 11/13] mm: Iterate only over charged shrinkers during memcg shrink_slab() Kirill Tkhai
2018-05-15 5:44 ` Vladimir Davydov
2018-05-15 10:12 ` Kirill Tkhai
2018-05-17 4:33 ` Vladimir Davydov
2018-05-17 11:39 ` Kirill Tkhai
2018-05-15 14:49 ` Kirill Tkhai
2018-05-17 4:16 ` Vladimir Davydov
2018-05-17 11:49 ` Kirill Tkhai
2018-05-17 13:51 ` Vladimir Davydov
2018-05-10 9:54 ` [PATCH v5 12/13] mm: Add SHRINK_EMPTY shrinker methods return value Kirill Tkhai
2018-05-10 9:54 ` [PATCH v5 13/13] mm: Clear shrinker bit if there are no objects related to memcg Kirill Tkhai
2018-05-15 5:59 ` Vladimir Davydov [this message]
2018-05-15 8:55 ` Kirill Tkhai
2018-05-17 4:49 ` Vladimir Davydov
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