From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f197.google.com (mail-pf0-f197.google.com [209.85.192.197]) by kanga.kvack.org (Postfix) with ESMTP id ACB906B000D for ; Tue, 15 May 2018 06:12:31 -0400 (EDT) Received: by mail-pf0-f197.google.com with SMTP id r63-v6so12775869pfl.12 for ; Tue, 15 May 2018 03:12:31 -0700 (PDT) Received: from EUR01-DB5-obe.outbound.protection.outlook.com (mail-db5eur01on0108.outbound.protection.outlook.com. [104.47.2.108]) by mx.google.com with ESMTPS id d31-v6si533721pld.23.2018.05.15.03.12.29 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Tue, 15 May 2018 03:12:30 -0700 (PDT) Subject: Re: [PATCH v5 11/13] mm: Iterate only over charged shrinkers during memcg shrink_slab() References: <152594582808.22949.8353313986092337675.stgit@localhost.localdomain> <152594603565.22949.12428911301395699065.stgit@localhost.localdomain> <20180515054445.nhe4zigtelkois4p@esperanza> From: Kirill Tkhai Message-ID: Date: Tue, 15 May 2018 13:12:20 +0300 MIME-Version: 1.0 In-Reply-To: <20180515054445.nhe4zigtelkois4p@esperanza> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Vladimir Davydov 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 On 15.05.2018 08:44, Vladimir Davydov wrote: > On Thu, May 10, 2018 at 12:53:55PM +0300, Kirill Tkhai wrote: >> Using the preparations made in previous patches, in case of memcg >> shrink, we may avoid shrinkers, which are not set in memcg's shrinkers >> bitmap. To do that, we separate iterations over memcg-aware and >> !memcg-aware shrinkers, and memcg-aware shrinkers are chosen >> via for_each_set_bit() from the bitmap. In case of big nodes, >> having many isolated environments, this gives significant >> performance growth. See next patches for the details. >> >> Note, that the patch does not respect to empty memcg shrinkers, >> since we never clear the bitmap bits after we set it once. >> Their shrinkers will be called again, with no shrinked objects >> as result. This functionality is provided by next patches. >> >> Signed-off-by: Kirill Tkhai >> --- >> include/linux/memcontrol.h | 1 + >> mm/vmscan.c | 70 ++++++++++++++++++++++++++++++++++++++------ >> 2 files changed, 62 insertions(+), 9 deletions(-) >> >> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h >> index 82f892e77637..436691a66500 100644 >> --- a/include/linux/memcontrol.h >> +++ b/include/linux/memcontrol.h >> @@ -760,6 +760,7 @@ void mem_cgroup_split_huge_fixup(struct page *head); >> #define MEM_CGROUP_ID_MAX 0 >> >> struct mem_cgroup; >> +#define root_mem_cgroup NULL > > Let's instead export mem_cgroup_is_root(). In case if MEMCG is disabled > it will always return false. export == move to header file >> >> static inline bool mem_cgroup_disabled(void) >> { >> diff --git a/mm/vmscan.c b/mm/vmscan.c >> index d8a2870710e0..a2e38e05adb5 100644 >> --- a/mm/vmscan.c >> +++ b/mm/vmscan.c >> @@ -376,6 +376,7 @@ int prealloc_shrinker(struct shrinker *shrinker) >> goto free_deferred; >> } >> >> + INIT_LIST_HEAD(&shrinker->list); > > IMO this shouldn't be here, see my comment below. > >> return 0; >> >> free_deferred: >> @@ -547,6 +548,63 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl, >> return freed; >> } >> >> +#ifdef CONFIG_MEMCG_SHRINKER >> +static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid, >> + struct mem_cgroup *memcg, int priority) >> +{ >> + struct memcg_shrinker_map *map; >> + unsigned long freed = 0; >> + int ret, i; >> + >> + if (!memcg_kmem_enabled() || !mem_cgroup_online(memcg)) >> + return 0; >> + >> + if (!down_read_trylock(&shrinker_rwsem)) >> + return 0; >> + >> + /* >> + * 1)Caller passes only alive memcg, so map can't be NULL. >> + * 2)shrinker_rwsem protects from maps expanding. > > ^^ > Nit: space missing here :-) I don't understand what you mean here. Please, clarify... >> + */ >> + map = rcu_dereference_protected(MEMCG_SHRINKER_MAP(memcg, nid), true); >> + BUG_ON(!map); >> + >> + for_each_set_bit(i, map->map, memcg_shrinker_nr_max) { >> + struct shrink_control sc = { >> + .gfp_mask = gfp_mask, >> + .nid = nid, >> + .memcg = memcg, >> + }; >> + struct shrinker *shrinker; >> + >> + shrinker = idr_find(&shrinker_idr, i); >> + if (!shrinker) { >> + clear_bit(i, map->map); >> + continue; >> + } > > The shrinker must be memcg aware so please add > > BUG_ON((shrinker->flags & SHRINKER_MEMCG_AWARE) == 0); > >> + if (list_empty(&shrinker->list)) >> + continue; > > I don't like using shrinker->list as an indicator that the shrinker has > been initialized. IMO if you do need such a check, you should split > shrinker_idr registration in two steps - allocate a slot in 'prealloc' > and set the pointer in 'register'. However, can we really encounter an > unregistered shrinker here? AFAIU a bit can be set in the shrinker map > only after the corresponding shrinker has been initialized, no? 1)No, it's not so. Here is a race: cpu#0 cpu#1 cpu#2 prealloc_shrinker() prealloc_shrinker() memcg_expand_shrinker_maps() memcg_expand_one_shrinker_map() memset(&new->map, 0xff); do_shrink_slab() (on uninitialized LRUs) init LRUs register_shrinker_prepared() So, the check is needed. 2)Assigning NULL pointer can't be used here, since NULL pointer is already used to clear unregistered shrinkers from the map. See the check right after idr_find(). list_empty() is used since it's the already existing indicator, which does not require additional member in struct shrinker. >> + >> + ret = do_shrink_slab(&sc, shrinker, priority); >> + freed += ret; >> + >> + if (rwsem_is_contended(&shrinker_rwsem)) { >> + freed = freed ? : 1; >> + break; >> + } >> + } >> + >> + up_read(&shrinker_rwsem); >> + return freed; >> +} >> +#else /* CONFIG_MEMCG_SHRINKER */ >> +static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid, >> + struct mem_cgroup *memcg, int priority) >> +{ >> + return 0; >> +} >> +#endif /* CONFIG_MEMCG_SHRINKER */ >> + >> /** >> * shrink_slab - shrink slab caches >> * @gfp_mask: allocation context >> @@ -576,8 +634,8 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid, >> struct shrinker *shrinker; >> unsigned long freed = 0; >> >> - if (memcg && (!memcg_kmem_enabled() || !mem_cgroup_online(memcg))) >> - return 0; >> + if (memcg && memcg != root_mem_cgroup) > > if (!mem_cgroup_is_root(memcg)) > >> + return shrink_slab_memcg(gfp_mask, nid, memcg, priority); >> >> if (!down_read_trylock(&shrinker_rwsem)) >> goto out; >> @@ -589,13 +647,7 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid, >> .memcg = memcg, >> }; >> >> - /* >> - * If kernel memory accounting is disabled, we ignore >> - * SHRINKER_MEMCG_AWARE flag and call all shrinkers >> - * passing NULL for memcg. >> - */ >> - if (memcg_kmem_enabled() && >> - !!memcg != !!(shrinker->flags & SHRINKER_MEMCG_AWARE)) >> + if (!!memcg != !!(shrinker->flags & SHRINKER_MEMCG_AWARE)) >> continue; > > I want this check gone. It's easy to achieve, actually - just remove the > following lines from shrink_node() > > if (global_reclaim(sc)) > shrink_slab(sc->gfp_mask, pgdat->node_id, NULL, > sc->priority); > >> >> if (!(shrinker->flags & SHRINKER_NUMA_AWARE)) >>