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Fri, 23 Apr 2021 09:52:30 -0700 (PDT) From: Waiman Long X-Google-Original-From: Waiman Long Subject: Re: [PATCH-next v5 2/4] mm/memcg: Cache vmstat data in percpu memcg_stock_pcp To: Roman Gushchin , Waiman Long Cc: Johannes Weiner , Michal Hocko , Vladimir Davydov , Andrew Morton , Tejun Heo , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Vlastimil Babka , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org, Shakeel Butt , Muchun Song , Alex Shi , Chris Down , Yafang Shao , Wei Yang , Masayoshi Mizuma , Xing Zhengjun , Matthew Wilcox References: <20210420192907.30880-1-longman@redhat.com> <20210420192907.30880-3-longman@redhat.com> Message-ID: <6a261f7f-a127-a757-9f4c-4231823911c1@redhat.com> Date: Fri, 23 Apr 2021 12:52:29 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.9.0 MIME-Version: 1.0 In-Reply-To: Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=llong@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: EDE3E2000242 X-Stat-Signature: 4gja8g1uxgendpz7kdsxfenz5sh6oj6p Received-SPF: none (redhat.com>: No applicable sender policy available) receiver=imf11; identity=mailfrom; envelope-from=""; helo=us-smtp-delivery-124.mimecast.com; client-ip=170.10.133.124 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1619196739-740639 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 4/22/21 9:56 PM, Roman Gushchin wrote: > On Thu, Apr 22, 2021 at 12:58:52PM -0400, Waiman Long wrote: >> On 4/21/21 7:28 PM, Roman Gushchin wrote: >>> On Tue, Apr 20, 2021 at 03:29:05PM -0400, Waiman Long wrote: >>>> Before the new slab memory controller with per object byte charging, >>>> charging and vmstat data update happen only when new slab pages are >>>> allocated or freed. Now they are done with every kmem_cache_alloc() >>>> and kmem_cache_free(). This causes additional overhead for workloads >>>> that generate a lot of alloc and free calls. >>>> >>>> The memcg_stock_pcp is used to cache byte charge for a specific >>>> obj_cgroup to reduce that overhead. To further reducing it, this patch >>>> makes the vmstat data cached in the memcg_stock_pcp structure as well >>>> until it accumulates a page size worth of update or when other cached >>>> data change. Caching the vmstat data in the per-cpu stock eliminates two >>>> writes to non-hot cachelines for memcg specific as well as memcg-lruvecs >>>> specific vmstat data by a write to a hot local stock cacheline. >>>> >>>> On a 2-socket Cascade Lake server with instrumentation enabled and this >>>> patch applied, it was found that about 20% (634400 out of 3243830) >>>> of the time when mod_objcg_state() is called leads to an actual call >>>> to __mod_objcg_state() after initial boot. When doing parallel kernel >>>> build, the figure was about 17% (24329265 out of 142512465). So caching >>>> the vmstat data reduces the number of calls to __mod_objcg_state() >>>> by more than 80%. >>>> >>>> Signed-off-by: Waiman Long >>>> Reviewed-by: Shakeel Butt >>>> --- >>>> mm/memcontrol.c | 86 +++++++++++++++++++++++++++++++++++++++++++++++-- >>>> 1 file changed, 83 insertions(+), 3 deletions(-) >>>> >>>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >>>> index 7cd7187a017c..292b4783b1a7 100644 >>>> --- a/mm/memcontrol.c >>>> +++ b/mm/memcontrol.c >>>> @@ -782,8 +782,9 @@ void __mod_lruvec_kmem_state(void *p, enum node_stat_item idx, int val) >>>> rcu_read_unlock(); >>>> } >>>> -void mod_objcg_state(struct obj_cgroup *objcg, struct pglist_data *pgdat, >>>> - enum node_stat_item idx, int nr) >>>> +static inline void mod_objcg_mlstate(struct obj_cgroup *objcg, >>>> + struct pglist_data *pgdat, >>>> + enum node_stat_item idx, int nr) >>>> { >>>> struct mem_cgroup *memcg; >>>> struct lruvec *lruvec; >>>> @@ -791,7 +792,7 @@ void mod_objcg_state(struct obj_cgroup *objcg, struct pglist_data *pgdat, >>>> rcu_read_lock(); >>>> memcg = obj_cgroup_memcg(objcg); >>>> lruvec = mem_cgroup_lruvec(memcg, pgdat); >>>> - mod_memcg_lruvec_state(lruvec, idx, nr); >>>> + __mod_memcg_lruvec_state(lruvec, idx, nr); >>>> rcu_read_unlock(); >>>> } >>>> @@ -2059,7 +2060,10 @@ struct memcg_stock_pcp { >>>> #ifdef CONFIG_MEMCG_KMEM >>>> struct obj_cgroup *cached_objcg; >>>> + struct pglist_data *cached_pgdat; >>> I wonder if we want to have per-node counters instead? >>> That would complicate the initialization of pcp stocks a bit, >>> but might shave off some additional cpu time. >>> But we can do it later too. >>> >> A per node counter will certainly complicate the code and reduce the >> performance benefit too. > Hm, why? We wouldn't need to flush the stock if the release happens > on some other cpu not matching the current pgdat. I had actually experimented with just caching vmstat data for the local node only. It turned out the hit rate was a bit lower. That is why I keep the current approach and I need to do further investigation on a better approach. Cheers, Longman