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Tue, 28 Jul 2020 18:53:44 +0000 Date: Tue, 28 Jul 2020 11:53:41 -0700 From: Roman Gushchin To: Johannes Weiner CC: Andrew Morton , Michal Hocko , , , , Subject: Re: [PATCH] mm: memcontrol: don't count limit-setting reclaim as memory pressure Message-ID: <20200728185341.GA410810@carbon.DHCP.thefacebook.com> References: <20200728135210.379885-2-hannes@cmpxchg.org> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200728135210.379885-2-hannes@cmpxchg.org> X-ClientProxiedBy: BYAPR11CA0047.namprd11.prod.outlook.com (2603:10b6:a03:80::24) To BYAPR15MB4136.namprd15.prod.outlook.com (2603:10b6:a03:96::24) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from carbon.DHCP.thefacebook.com (2620:10d:c090:400::5:19ed) by BYAPR11CA0047.namprd11.prod.outlook.com (2603:10b6:a03:80::24) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3239.16 via Frontend Transport; Tue, 28 Jul 2020 18:53:44 +0000 X-Originating-IP: [2620:10d:c090:400::5:19ed] X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 74470a21-29cc-432b-d248-08d833278d80 X-MS-TrafficTypeDiagnostic: BYAPR15MB3480: X-MS-Exchange-Transport-Forked: True X-Microsoft-Antispam-PRVS: X-FB-Source: Internal X-MS-Oob-TLC-OOBClassifiers: OLM:7219; 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This is unexpected. It > specifically causes problems for senpai > (https://github.com/facebookincubator/senpai), which is an agent that > routinely adjusts the memory limits and performs associated reclaim > work in tens or even hundreds of cgroups running on the host. The > cgroup that senpai is running in itself will report elevated levels of > memory pressure, even though it itself is under no memory shortage or > any sort of distress. > > Move the psi annotation from the central cgroup reclaim function to > callsites in the allocation context, and thereby no longer count any > limit-setting reclaim as memory pressure. If the newly set limit > causes the workload inside the cgroup into direct reclaim, that of > course will continue to count as memory pressure. > > Signed-off-by: Johannes Weiner Reviewed-by: Roman Gushchin Thanks! > --- > mm/memcontrol.c | 12 +++++++++++- > mm/vmscan.c | 6 ------ > 2 files changed, 11 insertions(+), 7 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 805a44bf948c..8377640ad494 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -2233,11 +2233,18 @@ static void reclaim_high(struct mem_cgroup *memcg, > gfp_t gfp_mask) > { > do { > + unsigned long pflags; > + > if (page_counter_read(&memcg->memory) <= > READ_ONCE(memcg->memory.high)) > continue; > + > memcg_memory_event(memcg, MEMCG_HIGH); > + > + psi_memstall_enter(&pflags); > try_to_free_mem_cgroup_pages(memcg, nr_pages, gfp_mask, true); > + psi_memstall_leave(&pflags); > + > } while ((memcg = parent_mem_cgroup(memcg)) && > !mem_cgroup_is_root(memcg)); > } > @@ -2451,10 +2458,11 @@ static int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask, > int nr_retries = MEM_CGROUP_RECLAIM_RETRIES; > struct mem_cgroup *mem_over_limit; > struct page_counter *counter; > + enum oom_status oom_status; > unsigned long nr_reclaimed; > bool may_swap = true; > bool drained = false; > - enum oom_status oom_status; > + unsigned long pflags; > > if (mem_cgroup_is_root(memcg)) > return 0; > @@ -2514,8 +2522,10 @@ static int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask, > > memcg_memory_event(mem_over_limit, MEMCG_MAX); > > + psi_memstall_enter(&pflags); > nr_reclaimed = try_to_free_mem_cgroup_pages(mem_over_limit, nr_pages, > gfp_mask, may_swap); > + psi_memstall_leave(&pflags); > > if (mem_cgroup_margin(mem_over_limit) >= nr_pages) > goto retry; > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 749d239c62b2..742538543c79 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -3318,7 +3318,6 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg, > bool may_swap) > { > unsigned long nr_reclaimed; > - unsigned long pflags; > unsigned int noreclaim_flag; > struct scan_control sc = { > .nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX), > @@ -3339,17 +3338,12 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg, > struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask); > > set_task_reclaim_state(current, &sc.reclaim_state); > - > trace_mm_vmscan_memcg_reclaim_begin(0, sc.gfp_mask); > - > - psi_memstall_enter(&pflags); > noreclaim_flag = memalloc_noreclaim_save(); > > nr_reclaimed = do_try_to_free_pages(zonelist, &sc); > > memalloc_noreclaim_restore(noreclaim_flag); > - psi_memstall_leave(&pflags); > - > trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed); > set_task_reclaim_state(current, NULL); > > -- > 2.27.0 >