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Subject[v4 1/4] mm, oom: refactor the TIF_MEMDIE usage
Date
First, separate tsk_is_oom_victim() and TIF_MEMDIE flag checks:
let the first one indicate that a task is killed by the OOM killer,
and the second one indicate that a task has an access to the memory
reserves (with a hope to eliminate it later).

Second, set TIF_MEMDIE to all threads of an OOM victim process.

Third, to limit the number of processes which have an access to memory
reserves, let's keep an atomic pointer to a task, which grabbed it.

Signed-off-by: Roman Gushchin <guro@fb.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: David Rientjes <rientjes@google.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: kernel-team@fb.com
Cc: cgroups@vger.kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-mm@kvack.org
---
kernel/exit.c | 2 +-
mm/memcontrol.c | 2 +-
mm/oom_kill.c | 30 +++++++++++++++++++++++++-----
3 files changed, 27 insertions(+), 7 deletions(-)

diff --git a/kernel/exit.c b/kernel/exit.c
index 8f40bee5ba9d..d5f372a2a363 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -542,7 +542,7 @@ static void exit_mm(void)
task_unlock(current);
mm_update_next_owner(mm);
mmput(mm);
- if (test_thread_flag(TIF_MEMDIE))
+ if (tsk_is_oom_victim(current))
exit_oom_victim();
}

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index d61133e6af99..9085e55eb69f 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1896,7 +1896,7 @@ static int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
* bypass the last charges so that they can exit quickly and
* free their memory.
*/
- if (unlikely(test_thread_flag(TIF_MEMDIE) ||
+ if (unlikely(tsk_is_oom_victim(current) ||
fatal_signal_pending(current) ||
current->flags & PF_EXITING))
goto force;
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 9e8b4f030c1c..72de01be4d33 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -435,6 +435,8 @@ static DECLARE_WAIT_QUEUE_HEAD(oom_victims_wait);

static bool oom_killer_disabled __read_mostly;

+static struct task_struct *tif_memdie_owner;
+
#define K(x) ((x) << (PAGE_SHIFT-10))

/*
@@ -656,13 +658,24 @@ static void mark_oom_victim(struct task_struct *tsk)
struct mm_struct *mm = tsk->mm;

WARN_ON(oom_killer_disabled);
- /* OOM killer might race with memcg OOM */
- if (test_and_set_tsk_thread_flag(tsk, TIF_MEMDIE))
+
+ if (!cmpxchg(&tif_memdie_owner, NULL, current)) {
+ struct task_struct *t;
+
+ rcu_read_lock();
+ for_each_thread(current, t)
+ set_tsk_thread_flag(t, TIF_MEMDIE);
+ rcu_read_unlock();
+ }
+
+ /*
+ * OOM killer might race with memcg OOM.
+ * oom_mm is bound to the signal struct life time.
+ */
+ if (cmpxchg(&tsk->signal->oom_mm, NULL, mm))
return;

- /* oom_mm is bound to the signal struct life time. */
- if (!cmpxchg(&tsk->signal->oom_mm, NULL, mm))
- mmgrab(tsk->signal->oom_mm);
+ mmgrab(tsk->signal->oom_mm);

/*
* Make sure that the task is woken up from uninterruptible sleep
@@ -682,6 +695,13 @@ void exit_oom_victim(void)
{
clear_thread_flag(TIF_MEMDIE);

+ /*
+ * If current tasks if a thread, which initially
+ * received TIF_MEMDIE, clear tif_memdie_owner to
+ * give a next process a chance to capture it.
+ */
+ cmpxchg(&tif_memdie_owner, current, NULL);
+
if (!atomic_dec_return(&oom_victims))
wake_up_all(&oom_victims_wait);
}
--
2.13.3
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