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Date: Tue, 21 Oct 2014 17:37:41 +0200 From: Michal Hocko <mhocko@...e.cz> To: Vladimir Davydov <vdavydov@...allels.com> Cc: Andrew Morton <akpm@...ux-foundation.org>, Johannes Weiner <hannes@...xchg.org>, linux-mm@...ck.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH] memcg: remove mem_cgroup_reclaimable check from soft reclaim On Tue 21-10-14 17:15:50, Vladimir Davydov wrote: > mem_cgroup_reclaimable() checks whether a cgroup has reclaimable pages > on *any* NUMA node. However, the only place where it's called is > mem_cgroup_soft_reclaim(), which tries to reclaim memory from a > *specific* zone. So the way how it's used is incorrect - it will return > true even if the cgroup doesn't have pages on the zone we're scanning. > > I think we can get rid of this check completely, because > mem_cgroup_shrink_node_zone(), which is called by > mem_cgroup_soft_reclaim() if mem_cgroup_reclaimable() returns true, is > equivalent to shrink_lruvec(), which exits almost immediately if the > lruvec passed to it is empty. So there's no need to optimize anything > here. Besides, we don't have such a check in the general scan path > (shrink_zone) either. > > Signed-off-by: Vladimir Davydov <vdavydov@...allels.com> yeah, let's ditch it. It doesn't make any sense without checking the target zone and even then it is dubious bevause get_scan_count will give us 0 target on an empty lru list. Acked-by: Michal Hocko <mhocko@...e.cz> Thanks > --- > mm/memcontrol.c | 43 ------------------------------------------- > 1 file changed, 43 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 53393e27ff03..833b6a696aab 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -1799,52 +1799,11 @@ int mem_cgroup_select_victim_node(struct mem_cgroup *memcg) > memcg->last_scanned_node = node; > return node; > } > - > -/* > - * Check all nodes whether it contains reclaimable pages or not. > - * For quick scan, we make use of scan_nodes. This will allow us to skip > - * unused nodes. But scan_nodes is lazily updated and may not cotain > - * enough new information. We need to do double check. > - */ > -static bool mem_cgroup_reclaimable(struct mem_cgroup *memcg, bool noswap) > -{ > - int nid; > - > - /* > - * quick check...making use of scan_node. > - * We can skip unused nodes. > - */ > - if (!nodes_empty(memcg->scan_nodes)) { > - for (nid = first_node(memcg->scan_nodes); > - nid < MAX_NUMNODES; > - nid = next_node(nid, memcg->scan_nodes)) { > - > - if (test_mem_cgroup_node_reclaimable(memcg, nid, noswap)) > - return true; > - } > - } > - /* > - * Check rest of nodes. > - */ > - for_each_node_state(nid, N_MEMORY) { > - if (node_isset(nid, memcg->scan_nodes)) > - continue; > - if (test_mem_cgroup_node_reclaimable(memcg, nid, noswap)) > - return true; > - } > - return false; > -} > - > #else > int mem_cgroup_select_victim_node(struct mem_cgroup *memcg) > { > return 0; > } > - > -static bool mem_cgroup_reclaimable(struct mem_cgroup *memcg, bool noswap) > -{ > - return test_mem_cgroup_node_reclaimable(memcg, 0, noswap); > -} > #endif > > static int mem_cgroup_soft_reclaim(struct mem_cgroup *root_memcg, > @@ -1888,8 +1847,6 @@ static int mem_cgroup_soft_reclaim(struct mem_cgroup *root_memcg, > } > continue; > } > - if (!mem_cgroup_reclaimable(victim, false)) > - continue; > total += mem_cgroup_shrink_node_zone(victim, gfp_mask, false, > zone, &nr_scanned); > *total_scanned += nr_scanned; > -- > 1.7.10.4 > -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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