[patch 11/11] mm, memcg: allow system oom killer to be disabled

David Rientjes
2014-03-05T03:59:46Z

Now that system oom conditions can properly be handled from userspace,
allow the oom killer to be disabled. Otherwise, the kernel will
immediately kill a process and memory will be freed. The userspace oom
handler may have a different policy.

Signed-off-by: David Rientjes <rientjes@google.com>
---
Documentation/cgroups/memory.txt | 4 ++--
include/linux/memcontrol.h | 6 ++++++
mm/memcontrol.c | 11 ++++++++---
mm/oom_kill.c | 3 +++
4 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
--- a/Documentation/cgroups/memory.txt
+++ b/Documentation/cgroups/memory.txt
@@ -755,8 +755,8 @@ You can disable the OOM-killer by writing "1" to memory.oom_control file, as:

# echo 1 > memory.oom_control

-This operation is only allowed to the top cgroup of a sub-hierarchy and does
-not include the root memcg.
+This operation is only allowed to the top cgroup of a sub-hierarchy. If
+disabled for the root memcg, the system oom killer is disabled.
If OOM-killer is disabled, tasks under cgroup will hang/sleep
in memory cgroup's OOM-waitqueue when they request accountable memory.

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -159,6 +159,7 @@ bool mem_cgroup_oom_synchronize(bool wait);
extern bool mem_cgroup_alloc_use_oom_reserve(void);
extern u64 mem_cgroup_root_oom_reserve(void);
extern void mem_cgroup_root_oom_notify(void);
+extern bool mem_cgroup_root_oom_disable(void);

#ifdef CONFIG_MEMCG_SWAP
extern int do_swap_account;
@@ -415,6 +416,11 @@ static inline void mem_cgroup_root_oom_notify(void)
{
}

+static inline bool mem_cgroup_root_oom_disable(void)
+{
+ return false;
+}
+
static inline void mem_cgroup_inc_page_stat(struct page *page,
enum mem_cgroup_stat_index idx)
{
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5976,13 +5976,13 @@ static int mem_cgroup_oom_control_write(struct cgroup_subsys_state *css,
struct mem_cgroup *memcg = mem_cgroup_from_css(css);
struct mem_cgroup *parent = mem_cgroup_from_css(css_parent(&memcg->css));

- /* cannot set to root cgroup and only 0 and 1 are allowed */
- if (!parent || !((val == 0) || (val == 1)))
+ /* only 0 and 1 are allowed */
+ if (val != !!val)
return -EINVAL;

mutex_lock(&memcg_create_mutex);
/* oom-kill-disable is a flag for subhierarchy. */
- if ((parent->use_hierarchy) || memcg_has_children(memcg)) {
+ if (parent && (parent->use_hierarchy || memcg_has_children(memcg))) {
mutex_unlock(&memcg_create_mutex);
return -EINVAL;
}
@@ -6062,6 +6062,11 @@ u64 mem_cgroup_root_oom_reserve(void)
return root_mem_cgroup->oom_reserve >> PAGE_SHIFT;
}

+bool mem_cgroup_root_oom_disable(void)
+{
+ return root_mem_cgroup->oom_kill_disable;
+}
+
#ifdef CONFIG_MEMCG_KMEM
static int memcg_init_kmem(struct mem_cgroup *memcg, struct cgroup_subsys *ss)
{
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -656,6 +656,9 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
mpol_mask = (constraint == CONSTRAINT_MEMORY_POLICY) ? nodemask : NULL;
check_panic_on_oom(constraint, gfp_mask, order, mpol_mask);

+ if (mem_cgroup_root_oom_disable())
+ return;
+
if (sysctl_oom_kill_allocating_task && current->mm &&
!oom_unkillable_task(current, NULL, nodemask) &&
current->signal->oom_score_adj != OOM_SCORE_ADJ_MIN) {