On 08/16/2016 08:07 AM, Joonsoo Kim wrote:

quoted

Signed-off-by: Vlastimil Babka <redacted>
---
 mm/page_alloc.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index fb975cec3518..b28517b918b0 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c

@@ -3155,13 +3155,8 @@ should_compact_retry(struct alloc_context *ac, int order, int alloc_flags,
 	 * so it doesn't really make much sense to retry except when the
 	 * failure could be caused by insufficient priority
 	 */
-	if (compaction_failed(compact_result)) {
-		if (*compact_priority > MIN_COMPACT_PRIORITY) {
-			(*compact_priority)--;
-			return true;
-		}
-		return false;
-	}
+	if (compaction_failed(compact_result))
+		goto check_priority;

 	/*
 	 * make sure the compaction wasn't deferred or didn't bail out early

@@ -3185,6 +3180,15 @@ should_compact_retry(struct alloc_context *ac, int order, int alloc_flags,
 	if (compaction_retries <= max_retries)
 		return true;

+	/*
+	 * Make sure there is at least one attempt at the highest priority
+	 * if we exhausted all retries at the lower priorities
+	 */
+check_priority:
+	if (*compact_priority > MIN_COMPACT_PRIORITY) {
+		(*compact_priority)--;
+		return true;
+	}
 	return false;

The only difference that this patch makes is increasing priority when
COMPACT_PARTIAL(COMPACTION_SUCCESS) returns. In that case, we can

Hm it's true that I adjusted this patch from the previous version, 
before realizing that PARTIAL is now SUCCESS.

usually allocate high-order freepage so we would not enter here. Am I
missing something? Is it really needed behaviour change?

It will likely be rare when this triggers, when compaction success 
doesn't lead to allocation success due to parallel allocation activity.

Thanks.

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