Re: [PATCH 2/2] mm: oom: deduplicate victim selection code for memcg and global oom

From: Tetsuo Handa
Date: Wed Jun 08 2016 - 07:18:58 EST


Michal Hocko wrote:
> The victim selection code can be reduced because it is basically
> shared between the two, only the iterator differs. But I guess that
> can be eliminated by a simple helper.

Thank you for CC: me. I like this clean up.

> ---
> include/linux/oom.h | 5 +++++
> mm/memcontrol.c | 47 ++++++-----------------------------------
> mm/oom_kill.c | 60 ++++++++++++++++++++++++++++-------------------------
> 3 files changed, 43 insertions(+), 69 deletions(-)

I think we can apply your version with below changes folded into your version.
(I think totalpages argument can be passed via oom_control as well. Also, according to
http://lkml.kernel.org/r/201602192336.EJF90671.HMFLFSVOFJOtOQ@xxxxxxxxxxxxxxxxxxx ,
we can safely replace oc->memcg in oom_badness() in oom_evaluate_task() with NULL. )

include/linux/oom.h | 10 ----------
mm/memcontrol.c | 7 +++++--
mm/oom_kill.c | 14 ++++++++++++--
3 files changed, 17 insertions(+), 14 deletions(-)

diff --git a/include/linux/oom.h b/include/linux/oom.h
index 7b3eb25..77e98a0 100644
--- a/include/linux/oom.h
+++ b/include/linux/oom.h
@@ -49,13 +49,6 @@ enum oom_constraint {
CONSTRAINT_MEMCG,
};

-enum oom_scan_t {
- OOM_SCAN_OK, /* scan thread and find its badness */
- OOM_SCAN_CONTINUE, /* do not consider thread for oom kill */
- OOM_SCAN_ABORT, /* abort the iteration and return */
- OOM_SCAN_SELECT, /* always select this thread first */
-};
-
extern struct mutex oom_lock;

static inline void set_current_oom_origin(void)
@@ -96,9 +89,6 @@ extern void oom_kill_process(struct oom_control *oc, struct task_struct *p,
extern void check_panic_on_oom(struct oom_control *oc,
enum oom_constraint constraint);

-extern enum oom_scan_t oom_scan_process_thread(struct oom_control *oc,
- struct task_struct *task);
-
extern bool out_of_memory(struct oom_control *oc);

extern void exit_oom_victim(struct task_struct *tsk);
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 9c51b4d..f3482a2 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1288,12 +1288,15 @@ static bool mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask,

css_task_iter_start(&iter->css, &it);
while ((task = css_task_iter_next(&it)))
- if (!oom_evaluate_task(&oc, task, totalpages))
+ if (!oom_evaluate_task(&oc, task, totalpages)) {
+ css_task_iter_end(&it);
+ mem_cgroup_iter_break(memcg, iter);
break;
+ }
css_task_iter_end(&it);
}

- if (oc.chosen) {
+ if (oc.chosen && oc.chosen != (void *) -1UL) {
points = oc.chosen_points * 1000 / totalpages;
oom_kill_process(&oc, oc.chosen, points, totalpages,
"Memory cgroup out of memory");
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index bce3ea2..f634bca 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -273,8 +273,15 @@ static enum oom_constraint constrained_alloc(struct oom_control *oc,
}
#endif

-enum oom_scan_t oom_scan_process_thread(struct oom_control *oc,
- struct task_struct *task)
+enum oom_scan_t {
+ OOM_SCAN_OK, /* scan thread and find its badness */
+ OOM_SCAN_CONTINUE, /* do not consider thread for oom kill */
+ OOM_SCAN_ABORT, /* abort the iteration and return */
+ OOM_SCAN_SELECT, /* always select this thread first */
+};
+
+static enum oom_scan_t oom_scan_process_thread(struct oom_control *oc,
+ struct task_struct *task)
{
if (oom_unkillable_task(task, NULL, oc->nodemask))
return OOM_SCAN_CONTINUE;
@@ -307,6 +314,9 @@ int oom_evaluate_task(struct oom_control *oc, struct task_struct *p, unsigned lo
case OOM_SCAN_CONTINUE:
return 1;
case OOM_SCAN_ABORT:
+ if (oc->chosen)
+ put_task_struct(oc->chosen);
+ oc->chosen = (void *) -1UL;
return 0;
case OOM_SCAN_OK:
break;