oom, trace: add compaction retry tracepoint

Higher order requests oom debugging is currently quite hard.  We do have
some compaction points which can tell us how the compaction is operating
but there is no trace point to tell us about compaction retry logic.
This patch adds a one which will have the following format

            bash-3126  [001] ....  1498.220001: compact_retry: order=9 priority=COMPACT_PRIO_SYNC_LIGHT compaction_result=withdrawn retries=0 max_retries=16 should_retry=0

we can see that the order 9 request is not retried even though we are in
the highest compaction priority mode becase the last compaction attempt
was withdrawn.  This means that compaction_zonelist_suitable must have
returned false and there is no suitable zone to compact for this request
and so no need to retry further.

another example would be
           <...>-3137  [001] ....    81.501689: compact_retry: order=9 priority=COMPACT_PRIO_SYNC_LIGHT compaction_result=failed retries=0 max_retries=16 should_retry=0

in this case the order-9 compaction failed to find any suitable block.
We do not retry anymore because this is a costly request and those do
not go below COMPACT_PRIO_SYNC_LIGHT priority.

Link: http://lkml.kernel.org/r/20161220130135.15719-4-mhocko@kernel.org
Signed-off-by: Michal Hocko <mhocko@suse.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: David Rientjes <rientjes@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 16 insertions, 6 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d20f8c3139bb..05c0a59323bd 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3197,6 +3197,9 @@ should_compact_retry(struct alloc_context *ac, int order, int alloc_flags,
 {
         int max_retries = MAX_COMPACT_RETRIES;
         int min_priority;
+        bool ret = false;
+        int retries = *compaction_retries;
+        enum compact_priority priority = *compact_priority;
 
         if (!order)
                 return false;
@@ -3218,8 +3221,10 @@ should_compact_retry(struct alloc_context *ac, int order, int alloc_flags,
          * But do not retry if the given zonelist is not suitable for
          * compaction.
          */
-        if (compaction_withdrawn(compact_result))
-                return compaction_zonelist_suitable(ac, order, alloc_flags);
+        if (compaction_withdrawn(compact_result)) {
+                ret = compaction_zonelist_suitable(ac, order, alloc_flags);
+                goto out;
+        }
 
         /*
          * !costly requests are much more important than __GFP_REPEAT
@@ -3231,8 +3236,10 @@ should_compact_retry(struct alloc_context *ac, int order, int alloc_flags,
          */
         if (order > PAGE_ALLOC_COSTLY_ORDER)
                 max_retries /= 4;
-        if (*compaction_retries <= max_retries)
-                return true;
+        if (*compaction_retries <= max_retries) {
+                ret = true;
+                goto out;
+        }
 
         /*
          * Make sure there are attempts at the highest priority if we exhausted
@@ -3241,12 +3248,15 @@ should_compact_retry(struct alloc_context *ac, int order, int alloc_flags,
 check_priority:
         min_priority = (order > PAGE_ALLOC_COSTLY_ORDER) ?
                         MIN_COMPACT_COSTLY_PRIORITY : MIN_COMPACT_PRIORITY;
+
         if (*compact_priority > min_priority) {
                 (*compact_priority)--;
                 *compaction_retries = 0;
-                return true;
+                ret = true;
         }
-        return false;
+out:
+        trace_compact_retry(order, priority, compact_result, retries, max_retries, ret);
+        return ret;
 }
 #else
 static inline struct page *