mm, oom: remove oom_lock from oom_reaper (af5679fb) · Commits · 戴 / test

oom_reaper used to rely on the oom_lock since ("oom_reaper: close race with exiting task"). We do not really need the lock anymore though. ("mm: oom: let oom_reap_task and exit_mmap run concurrently") has removed serialization with the exit path based on the mm reference count and so we do not really rely on the oom_lock anymore. Tetsuo was arguing that at least MMF_OOM_SKIP should be set under the lock to prevent from races when the page allocator didn't manage to get the freed (reaped) memory in __alloc_pages_may_oom but it sees the flag later on and move on to another victim. Although this is possible in principle let's wait for it to actually happen in real life before we make the locking more complex again. Therefore remove the oom_lock for oom_reaper paths (both exit_mmap and oom_reap_task_mm). The reaper serializes with exit_mmap by mmap_sem + MMF_OOM_SKIP flag. There is no synchronization with out_of_memory path now. [mhocko@kernel.org: oom_reap_task_mm should return false when __oom_reap_task_mm did] Link: http://lkml.kernel.org/r/20180724141747.GP28386@dhcp22.suse.cz Link: http://lkml.kernel.org/r/20180719075922.13784-1-mhocko@kernel.org Signed-off-by:

Michal Hocko <mhocko@suse.com> Suggested-by:

David Rientjes <rientjes@google.com> Acked-by:

David Rientjes <rientjes@google.com> Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

mm/mmap.c

+0 −2

Original line number	Diff line number	Diff line
		@@ -3063,9 +3063,7 @@ void exit_mmap(struct mm_struct *mm)
		* which clears VM_LOCKED, otherwise the oom reaper cannot
		* reliably test it.
		*/
		mutex_lock(&oom_lock);
		(void)__oom_reap_task_mm(mm);
		mutex_unlock(&oom_lock);

		set_bit(MMF_OOM_SKIP, &mm->flags);
		down_write(&mm->mmap_sem);

mm/oom_kill.c

+4 −26

Original line number	Diff line number	Diff line
		@@ -535,28 +535,9 @@ bool __oom_reap_task_mm(struct mm_struct *mm)

		static bool oom_reap_task_mm(struct task_struct tsk, struct mm_struct mm)
		{
		bool ret = true;

		/*
		* We have to make sure to not race with the victim exit path
		* and cause premature new oom victim selection:
		* oom_reap_task_mm exit_mm
		* mmget_not_zero
		* mmput
		* atomic_dec_and_test
		* exit_oom_victim
		* [...]
		* out_of_memory
		* select_bad_process
		* # no TIF_MEMDIE task selects new victim
		* unmap_page_range # frees some memory
		*/
		mutex_lock(&oom_lock);

		if (!down_read_trylock(&mm->mmap_sem)) {
		ret = false;
		trace_skip_task_reaping(tsk->pid);
		goto unlock_oom;
		return false;
		}

		/*
		@@ -568,7 +549,7 @@ static bool oom_reap_task_mm(struct task_struct tsk, struct mm_struct mm)
		if (test_bit(MMF_OOM_SKIP, &mm->flags)) {
		up_read(&mm->mmap_sem);
		trace_skip_task_reaping(tsk->pid);
		goto unlock_oom;
		return true;
		}

		trace_start_task_reaping(tsk->pid);
		@@ -576,8 +557,7 @@ static bool oom_reap_task_mm(struct task_struct tsk, struct mm_struct mm)
		/* failed to reap part of the address space. Try again later */
		if (!__oom_reap_task_mm(mm)) {
		up_read(&mm->mmap_sem);
		ret = false;
		goto unlock_oom;
		return false;
		}

		pr_info("oom_reaper: reaped process %d (%s), now anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB\n",
		@@ -588,9 +568,7 @@ static bool oom_reap_task_mm(struct task_struct tsk, struct mm_struct mm)
		up_read(&mm->mmap_sem);

		trace_finish_task_reaping(tsk->pid);
		unlock_oom:
		mutex_unlock(&oom_lock);
		return ret;
		return true;
		}

		#define MAX_OOM_REAP_RETRIES 10

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