memcg: remove mem_cgroup_reclaimable check from soft reclaim (4ef461e8) · Commits · 戴 / test

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 it is 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@parallels.com> Acked-by:

Michal Hocko <mhocko@suse.cz> Acked-by:

Johannes Weiner <hannes@cmpxchg.org> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

mm/memcontrol.c

+0 −43

Original line number	Diff line number	Diff line
		@@ -1743,52 +1743,11 @@ 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,
		@@ -1832,8 +1791,6 @@ 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;

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