On Thu, Mar 26, 2015 at 03:32:23PM +0100, Michal Hocko wrote:

On Thu 26-03-15 07:24:45, Johannes Weiner wrote:

quoted

On Wed, Mar 25, 2015 at 11:15:48PM +0900, Tetsuo Handa wrote:

quoted

Johannes Weiner wrote:

[...]

quoted

quoted

quoted

 	/*
-	 * Acquire the oom lock.  If that fails, somebody else is
-	 * making progress for us.
+	 * This allocating task can become the OOM victim itself at
+	 * any point before acquiring the lock.  In that case, exit
+	 * quickly and don't block on the lock held by another task
+	 * waiting for us to exit.
 	 */
-	if (!mutex_trylock(&oom_lock)) {
-		*did_some_progress = 1;
-		schedule_timeout_uninterruptible(1);
-		return NULL;
+	if (test_thread_flag(TIF_MEMDIE) || mutex_lock_killable(&oom_lock)) {
+		alloc_flags |= ALLOC_NO_WATERMARKS;
+		goto alloc;
 	}

When a thread group has 1000 threads and most of them are doing memory allocation
request, all of them will get fatal_signal_pending() == true when one of them are
chosen by OOM killer.
This code will allow most of them to access memory reserves, won't it?

Ah, good point!  Only TIF_MEMDIE should get reserve access, not just
any dying thread.  Thanks, I'll fix it in v2.

Do you plan to post this v2 here for review?

Yeah, I was going to wait for feedback to settle before updating the
code.  But I was thinking something like this?

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 9ce9c4c083a0..106793a75461 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c

@@ -2344,7 +2344,8 @@ __alloc_pages_may_oom(gfp_t gfp_mask, unsigned int order, int alloc_flags,
 	 * waiting for us to exit.
 	 */
 	if (test_thread_flag(TIF_MEMDIE) || mutex_lock_killable(&oom_lock)) {
-		alloc_flags |= ALLOC_NO_WATERMARKS;
+		if (test_thread_flag(TIF_MEMDIE))
+			alloc_flags |= ALLOC_NO_WATERMARKS;
 		goto alloc;
 	}
 

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