[PATCH 00/11] kmem controller for memcg: stripped down version

The current memcg slab cache management fails to present satisfatory hierarchical
behavior in the following scenario:

-> /cgroups/memory/A/B/C

* kmem limit set at A
* A and B empty taskwise
* bash in C does find /

Because kmem_accounted is a boolean that was not set for C, no accounting
would be done. This is, however, not what we expect.

The basic idea, is that when a cgroup is limited, we walk the tree
upwards (something Kame and I already thought about doing for other purposes),
and make sure that we store the information about the parent being limited in
kmem_accounted (that is turned into a bitmap: two booleans would not be space
efficient). The code for that is taken from sched/core.c. My reasons for not
putting it into a common place is to dodge the type issues that would arise
from a common implementation between memcg and the scheduler - but I think
that it should ultimately happen, so if you want me to do it now, let me
know.

We do the reverse operation when a formerly limited cgroup becomes unlimited.

Signed-off-by: Glauber Costa
CC: Christoph Lameter
CC: Pekka Enberg
CC: Michal Hocko
CC: Kamezawa Hiroyuki
CC: Johannes Weiner
CC: Suleiman Souhlal

mm/memcontrol.c | 86 +++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 71 insertions(+), 15 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index fe5388e..a6a440b 100644
a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -287,7 +287,11 @@ struct mem_cgroup {
* Should the accounting and control be hierarchical, per subtree?
*/
bool use_hierarchy;
- bool kmem_accounted;
+ /*
+ * bit0: accounted by this cgroup
+ * bit1: accounted by a parent.
+ */
+ volatile unsigned long kmem_accounted;

bool oom_lock;
atomic_t under_oom;
@@ -340,6 +344,9 @@ struct mem_cgroup {
#endif
};

+#define KMEM_ACCOUNTED_THIS 0
+#define KMEM_ACCOUNTED_PARENT 1
+
/* Stuffs for move charges at task migration. */
/*
* Types of charges to be moved. "move_charge_at_immitgrate" is treated as a
@@ -589,7 +596,7 @@ EXPORT_SYMBOL(__mem_cgroup_free_kmem_page);

static void disarm_kmem_keys(struct mem_cgroup *memcg)
{
- if (memcg->kmem_accounted)
+ if (test_bit(KMEM_ACCOUNTED_THIS, &memcg->kmem_accounted))
static_key_slow_dec(&mem_cgroup_kmem_enabled_key);
}
#else
@@ -4027,6 +4034,66 @@ static ssize_t mem_cgroup_read(struct cgroup *cont, struct cftype *cft,
len = scnprintf(str, sizeof(str), "%llu", (unsigned long long)val);
return simple_read_from_buffer(buf, nbytes, ppos, str, len);
}
+
+#ifdef CONFIG_CGROUP_MEM_RES_CTLR_KMEM
+static void mem_cgroup_update_kmem_limit(struct mem_cgroup *memcg, u64 val)
+{
+ struct mem_cgroup *iter;
+
+ mutex_lock(&set_limit_mutex);
+ if (!test_and_set_bit(KMEM_ACCOUNTED_THIS, &memcg->kmem_accounted) &&
+ val != RESOURCE_MAX) {
+
+ /*
+ * Once enabled, can't be disabled. We could in theory
+ * disable it if we haven't yet created any caches, or
+ * if we can shrink them all to death.
+ *
+ * But it is not worth the trouble
+ */
+ static_key_slow_inc(&mem_cgroup_kmem_enabled_key);
+
+ if (!memcg->use_hierarchy)
+ goto out;
+
+ for_each_mem_cgroup_tree(iter, memcg) {
+ if (iter == memcg)
+ continue;
+ set_bit(KMEM_ACCOUNTED_PARENT, &iter->kmem_accounted);
+ }
+
+ } else if (test_and_clear_bit(KMEM_ACCOUNTED_THIS, &memcg->kmem_accounted)
+ && val == RESOURCE_MAX) {
+
+ if (!memcg->use_hierarchy)
+ goto out;
+
+ for_each_mem_cgroup_tree(iter, memcg) {
+ struct mem_cgroup *parent;
+ if (iter == memcg)
+ continue;
+ /*
+ * We should only have our parent bit cleared if none of
+ * ouri parents are accounted. The transversal order of
+ * our iter function forces us to always look at the
+ * parents.
+ */
+ parent = parent_mem_cgroup(iter);
+ while (parent && (parent != memcg)) {
+ if (test_bit(KMEM_ACCOUNTED_THIS, &parent->kmem_accounted))
+ goto noclear;
+
+ parent = parent_mem_cgroup(parent);
+ }
+ clear_bit(KMEM_ACCOUNTED_PARENT, &iter->kmem_accounted);
+noclear:
+ continue;
+ }
+ }
+out:
+ mutex_unlock(&set_limit_mutex);
+}
+#endif
/*
* The user of this function is...
* RES_LIMIT.
@@ -4064,19 +4131,8 @@ static int mem_cgroup_write(struct cgroup *cont, struct cftype *cft,
ret = res_counter_set_limit(&memcg->kmem, val);
if (ret)
break;
- /*
- * Once enabled, can't be disabled. We could in theory
- * disable it if we haven't yet created any caches, or
- * if we can shrink them all to death.
- *
- * But it is not worth the trouble
- */
- mutex_lock(&set_limit_mutex);
- if (!memcg->kmem_accounted && val != RESOURCE_MAX) {
- static_key_slow_inc(&mem_cgroup_kmem_enabled_key);
- memcg->kmem_accounted = true;
- }
- mutex_unlock(&set_limit_mutex);
+ mem_cgroup_update_kmem_limit(memcg, val);
+ break;
}
#endif
else
1.7.10.2

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