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[185.231.240.75]) by mx.google.com with ESMTPS id p69si9644904ljb.75.2019.02.26.04.50.15 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 26 Feb 2019 04:50:15 -0800 (PST) Received-SPF: pass (google.com: domain of aryabinin@virtuozzo.com designates 185.231.240.75 as permitted sender) client-ip=185.231.240.75; Authentication-Results: mx.google.com; spf=pass (google.com: domain of aryabinin@virtuozzo.com designates 185.231.240.75 as permitted sender) smtp.mailfrom=aryabinin@virtuozzo.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=virtuozzo.com Received: from [172.16.25.12] by relay.sw.ru with esmtp (Exim 4.91) (envelope-from ) id 1gycBM-0007rk-W3; Tue, 26 Feb 2019 15:50:01 +0300 Subject: Re: [PATCH RFC] mm/vmscan: try to protect active working set of cgroup from reclaim. To: Johannes Weiner Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Michal Hocko , Vlastimil Babka , Rik van Riel , Mel Gorman , Roman Gushchin , Shakeel Butt References: <20190222175825.18657-1-aryabinin@virtuozzo.com> <20190222191552.GA15922@cmpxchg.org> From: Andrey Ryabinin Message-ID: Date: Tue, 26 Feb 2019 15:50:19 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.1 MIME-Version: 1.0 In-Reply-To: <20190222191552.GA15922@cmpxchg.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit 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 2/22/19 10:15 PM, Johannes Weiner wrote: > On Fri, Feb 22, 2019 at 08:58:25PM +0300, Andrey Ryabinin wrote: >> In a presence of more than 1 memory cgroup in the system our reclaim >> logic is just suck. When we hit memory limit (global or a limit on >> cgroup with subgroups) we reclaim some memory from all cgroups. >> This is sucks because, the cgroup that allocates more often always wins. >> E.g. job that allocates a lot of clean rarely used page cache will push >> out of memory other jobs with active relatively small all in memory >> working set. >> >> To prevent such situations we have memcg controls like low/max, etc which >> are supposed to protect jobs or limit them so they to not hurt others. >> But memory cgroups are very hard to configure right because it requires >> precise knowledge of the workload which may vary during the execution. >> E.g. setting memory limit means that job won't be able to use all memory >> in the system for page cache even if the rest the system is idle. >> Basically our current scheme requires to configure every single cgroup >> in the system. >> >> I think we can do better. The idea proposed by this patch is to reclaim >> only inactive pages and only from cgroups that have big >> (!inactive_is_low()) inactive list. And go back to shrinking active lists >> only if all inactive lists are low. > > Yes, you are absolutely right. > > We shouldn't go after active pages as long as there are plenty of > inactive pages around. That's the global reclaim policy, and we > currently fail to translate that well to cgrouped systems. > > Setting group protections or limits would work around this problem, > but they're kind of a red herring. We shouldn't ever allow use-once > streams to push out hot workingsets, that's a bug. > >> @@ -2489,6 +2491,10 @@ static void get_scan_count(struct lruvec *lruvec, struct mem_cgroup *memcg, >> >> scan >>= sc->priority; >> >> + if (!sc->may_shrink_active && inactive_list_is_low(lruvec, >> + file, memcg, sc, false)) >> + scan = 0; >> + >> /* >> * If the cgroup's already been deleted, make sure to >> * scrape out the remaining cache. >> @@ -2733,6 +2739,7 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc) >> struct reclaim_state *reclaim_state = current->reclaim_state; >> unsigned long nr_reclaimed, nr_scanned; >> bool reclaimable = false; >> + bool retry; >> >> do { >> struct mem_cgroup *root = sc->target_mem_cgroup; >> @@ -2742,6 +2749,8 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc) >> }; >> struct mem_cgroup *memcg; >> >> + retry = false; >> + >> memset(&sc->nr, 0, sizeof(sc->nr)); >> >> nr_reclaimed = sc->nr_reclaimed; >> @@ -2813,6 +2822,13 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc) >> } >> } while ((memcg = mem_cgroup_iter(root, memcg, &reclaim))); >> >> + if ((sc->nr_scanned - nr_scanned) == 0 && >> + !sc->may_shrink_active) { >> + sc->may_shrink_active = 1; >> + retry = true; >> + continue; >> + } > > Using !scanned as the gate could be a problem. There might be a cgroup > that has inactive pages on the local level, but when viewed from the > system level the total inactive pages in the system might still be low > compared to active ones. In that case we should go after active pages. > > Basically, during global reclaim, the answer for whether active pages > should be scanned or not should be the same regardless of whether the > memory is all global or whether it's spread out between cgroups. > > The reason this isn't the case is because we're checking the ratio at > the lruvec level - which is the highest level (and identical to the > node counters) when memory is global, but it's at the lowest level > when memory is cgrouped. > > So IMO what we should do is: > > - At the beginning of global reclaim, use node_page_state() to compare > the INACTIVE_FILE:ACTIVE_FILE ratio and then decide whether reclaim > can go after active pages or not. Regardless of what the ratio is in > individual lruvecs. > > - And likewise at the beginning of cgroup limit reclaim, walk the > subtree starting at sc->target_mem_cgroup, sum up the INACTIVE_FILE > and ACTIVE_FILE counters, and make inactive_is_low() decision on > those sums. > Sounds reasonable.