Re: How to handle TIF_MEMDIE stalls?

[Michal Hocko <mhocko@xxxxxxx>]

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