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memcg: remove mem_cgroup_reclaimable check from soft reclaim

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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>
This commit is contained in:
Vladimir Davydov 2014-12-10 15:44:16 -08:00 committed by Linus Torvalds
parent 97ad2be1da
commit 4ef461e8f4
1 changed files with 0 additions and 43 deletions
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43
mm/memcontrol.c
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@ -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;