>From 70de3fe92435095b6ecbb400c61e84a99f639d56 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Date: Fri, 8 Jul 2016 00:28:12 +0900
Subject: [PATCH 1/6] mm,oom_reaper: Reduce find_lock_task_mm() usage.
Since holding mm_struct with elevated mm_count for a second is harmless,
we can determine mm_struct and hold it upon entry of oom_reap_task().
This patch has no functional change. Future patch in this series will
eliminate find_lock_task_mm() usage from the OOM reaper.
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
---
mm/oom_kill.c | 79 ++++++++++++++++++++++++++++-------------------------------
1 file changed, 37 insertions(+), 42 deletions(-)
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 7d0a275..951eb1b 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -452,12 +452,10 @@ static DECLARE_WAIT_QUEUE_HEAD(oom_reaper_wait);
static struct task_struct *oom_reaper_list;
static DEFINE_SPINLOCK(oom_reaper_lock);
-static bool __oom_reap_task(struct task_struct *tsk)
+static bool __oom_reap_task(struct task_struct *tsk, struct mm_struct *mm)
{
struct mmu_gather tlb;
struct vm_area_struct *vma;
- struct mm_struct *mm = NULL;
- struct task_struct *p;
struct zap_details details = {.check_swap_entries = true,
.ignore_dirty = true};
bool ret = true;
@@ -478,22 +476,9 @@ static bool __oom_reap_task(struct task_struct *tsk)
*/
mutex_lock(&oom_lock);
- /*
- * Make sure we find the associated mm_struct even when the particular
- * thread has already terminated and cleared its mm.
- * We might have race with exit path so consider our work done if there
- * is no mm.
- */
- p = find_lock_task_mm(tsk);
- if (!p)
- goto unlock_oom;
- mm = p->mm;
- atomic_inc(&mm->mm_count);
- task_unlock(p);
-
if (!down_read_trylock(&mm->mmap_sem)) {
ret = false;
- goto mm_drop;
+ goto unlock_oom;
}
/*
@@ -503,7 +488,7 @@ static bool __oom_reap_task(struct task_struct *tsk)
*/
if (!mmget_not_zero(mm)) {
up_read(&mm->mmap_sem);
- goto mm_drop;
+ goto unlock_oom;
}
tlb_gather_mmu(&tlb, mm, 0, -1);
@@ -551,8 +536,6 @@ static bool __oom_reap_task(struct task_struct *tsk)
* put the oom_reaper out of the way.
*/
mmput_async(mm);
-mm_drop:
- mmdrop(mm);
unlock_oom:
mutex_unlock(&oom_lock);
return ret;
@@ -562,36 +545,45 @@ unlock_oom:
static void oom_reap_task(struct task_struct *tsk)
{
int attempts = 0;
+ struct mm_struct *mm = NULL;
+ struct task_struct *p = find_lock_task_mm(tsk);
+
+ /*
+ * Make sure we find the associated mm_struct even when the particular
+ * thread has already terminated and cleared its mm.
+ * We might have race with exit path so consider our work done if there
+ * is no mm.
+ */
+ if (!p)
+ goto done;
+ mm = p->mm;
+ atomic_inc(&mm->mm_count);
+ task_unlock(p);
/* Retry the down_read_trylock(mmap_sem) a few times */
- while (attempts++ < MAX_OOM_REAP_RETRIES && !__oom_reap_task(tsk))
+ while (attempts++ < MAX_OOM_REAP_RETRIES && !__oom_reap_task(tsk, mm))
schedule_timeout_idle(HZ/10);
- if (attempts > MAX_OOM_REAP_RETRIES) {
- struct task_struct *p;
+ if (attempts <= MAX_OOM_REAP_RETRIES)
+ goto done;
- pr_info("oom_reaper: unable to reap pid:%d (%s)\n",
- task_pid_nr(tsk), tsk->comm);
+ 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.
- */
- p = find_lock_task_mm(tsk);
- if (p) {
- if (test_and_set_bit(MMF_OOM_NOT_REAPABLE, &p->mm->flags)) {
- pr_info("oom_reaper: giving up pid:%d (%s)\n",
- task_pid_nr(tsk), tsk->comm);
- set_bit(MMF_OOM_REAPED, &p->mm->flags);
- }
- task_unlock(p);
- }
-
- debug_show_all_locks();
+ /*
+ * 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:
/*
* Clear TIF_MEMDIE because the task shouldn't be sitting on a
* reasonably reclaimable memory anymore or it is not a good candidate
@@ -603,6 +595,9 @@ static void oom_reap_task(struct task_struct *tsk)
/* Drop a reference taken by wake_oom_reaper */
put_task_struct(tsk);
+ /* Drop a reference taken above. */
+ if (mm)
+ mmdrop(mm);
}
static int oom_reaper(void *unused)
--
1.8.3.1
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