How to handle TIF_MEMDIE stalls?

[Michal Hocko]

On Thu 19-02-15 13:29:14, Michal Hocko wrote:
[...]
> Something like the following.
__GFP_HIGH doesn't seem to be sufficient so we would need something
slightly else but the idea is still the same:

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 8d52ab18fe0d..2d224bbdf8e8 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2599,6 +2599,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
 	enum migrate_mode migration_mode = MIGRATE_ASYNC;
 	bool deferred_compaction = false;
 	int contended_compaction = COMPACT_CONTENDED_NONE;
+	int oom = 0;
 
 	/*
 	 * In the slowpath, we sanity check order to avoid ever trying to
@@ -2635,6 +2636,15 @@ retry:
 	alloc_flags = gfp_to_alloc_flags(gfp_mask);
 
 	/*
+	 * __GFP_NOFAIL allocations cannot fail but yet the current context
+	 * might be blocking resources needed by the OOM victim to terminate.
+	 * Allow the caller to dive into memory reserves to succeed the
+	 * allocation and break out from a potential deadlock.
+	 */
+	if (oom > 10 && (gfp_mask & __GFP_NOFAIL))
+		alloc_flags |= ALLOC_NO_WATERMARKS;
+
+	/*
 	 * Find the true preferred zone if the allocation is unconstrained by
 	 * cpusets.
 	 */
@@ -2759,6 +2769,8 @@ retry:
 				goto got_pg;
 			if (!did_some_progress)
 				goto nopage;
+
+			oom++;
 		}
 		/* Wait for some write requests to complete then retry */
 		wait_iff_congested(ac->preferred_zone, BLK_RW_ASYNC, HZ/50);
-- 
Michal Hocko
SUSE Labs