mm,oom_reaper: do not attempt to reap a task twice

"mm, oom_reaper: do not attempt to reap a task twice" tried to give the
OOM reaper one more chance to retry using MMF_OOM_NOT_REAPABLE flag.
But the usefulness of the flag is rather limited and actually never
shown in practice.  If the flag is set, it means that the holder of
mm->mmap_sem cannot call up_write() due to presumably being blocked at
unkillable wait waiting for other thread's memory allocation.  But since
one of threads sharing that mm will queue that mm immediately via
task_will_free_mem() shortcut (otherwise, oom_badness() will select the
same mm again due to oom_score_adj value unchanged), retrying
MMF_OOM_NOT_REAPABLE mm is unlikely helpful.

Let's always set MMF_OOM_REAPED.

Link: http://lkml.kernel.org/r/1472119394-11342-3-git-send-email-mhocko@kernel.org
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Michal Hocko <mhocko@suse.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Vladimir Davydov <vdavydov@parallels.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 3 insertions, 13 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 7543a476178b..b48cd32be445 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -525,7 +525,6 @@ static inline int get_dumpable(struct mm_struct *mm)
 #define MMF_HAS_UPROBES         19      /* has uprobes */
 #define MMF_RECALC_UPROBES      20      /* MMF_HAS_UPROBES can be wrong */
 #define MMF_OOM_REAPED          21      /* mm has been already reaped */
-#define MMF_OOM_NOT_REAPABLE    22      /* mm couldn't be reaped */
 
 #define MMF_INIT_MASK           (MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK)
 
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 87fad956c96b..45097f5a8f30 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -578,20 +578,11 @@ static void oom_reap_task(struct task_struct *tsk)
         if (attempts <= MAX_OOM_REAP_RETRIES)
                 goto done;
 
+        /* Ignore this mm because somebody can't call up_write(mmap_sem). */
+        set_bit(MMF_OOM_REAPED, &mm->flags);
+
         pr_info("oom_reaper: unable to reap pid:%d (%s)\n",
                 task_pid_nr(tsk), tsk->comm);
-
-        /*
-         * If we've already tried to reap this task in the past and
-         * failed it probably doesn't make much sense to try yet again
-         * so hide the mm from the oom killer so that it can move on
-         * to another task with a different mm struct.
-         */
-        if (test_and_set_bit(MMF_OOM_NOT_REAPABLE, &mm->flags)) {
-                pr_info("oom_reaper: giving up pid:%d (%s)\n",
-                        task_pid_nr(tsk), tsk->comm);
-                set_bit(MMF_OOM_REAPED, &mm->flags);
-        }
         debug_show_all_locks();
 
 done: