diff options
authorMichal Hocko <mhocko@suse.cz>2014-06-06 14:38:15 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2014-06-06 16:08:17 -0700
commit688eb988d15af55c1d1b70b1ca9f6ce58f277c20 (patch)
parent722773afd83209d4088d30946bc274f547528a0b (diff)
vmscan: memcg: always use swappiness of the reclaimed memcg
Memory reclaim always uses swappiness of the reclaim target memcg (origin of the memory pressure) or vm_swappiness for global memory reclaim. This behavior was consistent (except for difference between global and hard limit reclaim) because swappiness was enforced to be consistent within each memcg hierarchy. After "mm: memcontrol: remove hierarchy restrictions for swappiness and oom_control" each memcg can have its own swappiness independent of hierarchical parents, though, so the consistency guarantee is gone. This can lead to an unexpected behavior. Say that a group is explicitly configured to not swapout by memory.swappiness=0 but its memory gets swapped out anyway when the memory pressure comes from its parent with a It is also unexpected that the knob is meaningless without setting the hard limit which would trigger the reclaim and enforce the swappiness. There are setups where the hard limit is configured higher in the hierarchy by an administrator and children groups are under control of somebody else who is interested in the swapout behavior but not necessarily about the memory limit. From a semantic point of view swappiness is an attribute defining anon vs. file proportional scanning of LRU which is memcg specific (unlike charges which are propagated up the hierarchy) so it should be applied to the particular memcg's LRU regardless where the memory pressure comes from. This patch removes vmscan_swappiness() and stores the swappiness into the scan_control structure. mem_cgroup_swappiness is then used to provide the correct value before shrink_lruvec is called. The global vm_swappiness is used for the root memcg. [hughd@google.com: oopses immediately when booted with cgroup_disable=memory] Signed-off-by: Michal Hocko <mhocko@suse.cz> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Cc: Tejun Heo <tj@kernel.org> Signed-off-by: Hugh Dickins <hughd@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
3 files changed, 16 insertions, 19 deletions
diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
index 4937e6fff9b4..b3429aec444c 100644
--- a/Documentation/cgroups/memory.txt
+++ b/Documentation/cgroups/memory.txt
@@ -540,14 +540,13 @@ Note:
5.3 swappiness
-Similar to /proc/sys/vm/swappiness, but only affecting reclaim that is
-triggered by this cgroup's hard limit. The tunable in the root cgroup
-corresponds to the global swappiness setting.
-Please note that unlike the global swappiness, memcg knob set to 0
-really prevents from any swapping even if there is a swap storage
-available. This might lead to memcg OOM killer if there are no file
-pages to reclaim.
+Overrides /proc/sys/vm/swappiness for the particular group. The tunable
+in the root cgroup corresponds to the global swappiness setting.
+Please note that unlike during the global reclaim, limit reclaim
+enforces that 0 swappiness really prevents from any swapping even if
+there is a swap storage available. This might lead to memcg OOM killer
+if there are no file pages to reclaim.
5.4 failcnt
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index a500cb0594c4..9bf8a84bcaae 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1550,7 +1550,7 @@ static unsigned long mem_cgroup_margin(struct mem_cgroup *memcg)
int mem_cgroup_swappiness(struct mem_cgroup *memcg)
/* root ? */
- if (!css_parent(&memcg->css))
+ if (mem_cgroup_disabled() || !css_parent(&memcg->css))
return vm_swappiness;
return memcg->swappiness;
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 05d41c0d7f6c..f44476a41544 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -83,6 +83,9 @@ struct scan_control {
/* Scan (total_size >> priority) pages at once */
int priority;
+ /* anon vs. file LRUs scanning "ratio" */
+ int swappiness;
* The memory cgroup that hit its limit and as a result is the
* primary target of this reclaim invocation.
@@ -1845,13 +1848,6 @@ static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
return shrink_inactive_list(nr_to_scan, lruvec, sc, lru);
-static int vmscan_swappiness(struct scan_control *sc)
- if (global_reclaim(sc))
- return vm_swappiness;
- return mem_cgroup_swappiness(sc->target_mem_cgroup);
enum scan_balance {
@@ -1912,7 +1908,7 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
* using the memory controller's swap limit feature would be
* too expensive.
- if (!global_reclaim(sc) && !vmscan_swappiness(sc)) {
+ if (!global_reclaim(sc) && !sc->swappiness) {
scan_balance = SCAN_FILE;
goto out;
@@ -1922,7 +1918,7 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
* system is close to OOM, scan both anon and file equally
* (unless the swappiness setting disagrees with swapping).
- if (!sc->priority && vmscan_swappiness(sc)) {
+ if (!sc->priority && sc->swappiness) {
scan_balance = SCAN_EQUAL;
goto out;
@@ -1965,7 +1961,7 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
* With swappiness at 100, anonymous and file have the same priority.
* This scanning priority is essentially the inverse of IO cost.
- anon_prio = vmscan_swappiness(sc);
+ anon_prio = sc->swappiness;
file_prio = 200 - anon_prio;
@@ -2265,6 +2261,7 @@ static void shrink_zone(struct zone *zone, struct scan_control *sc)
lruvec = mem_cgroup_zone_lruvec(zone, memcg);
+ sc->swappiness = mem_cgroup_swappiness(memcg);
shrink_lruvec(lruvec, sc);
@@ -2731,6 +2728,7 @@ unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *memcg,
.may_swap = !noswap,
.order = 0,
.priority = 0,
+ .swappiness = mem_cgroup_swappiness(memcg),
.target_mem_cgroup = memcg,
struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);

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