[PATCH 0/2] Follow-up to Leave IRQs enabled for per-cpu page allocations

[PATCH 0/2] Follow-up to Leave IRQs enabled for per-cpu page allocations

[Mel Gorman]

The following two patches are a fixup patch and a simplification as
suggested by Vlastimil Babka.

 mm/page_alloc.c | 29 +++++++++++------------------
 1 file changed, 11 insertions(+), 18 deletions(-)

-- 
2.35.3

[PATCH 1/2] mm/page_alloc: Leave IRQs enabled for per-cpu page allocations -fix

[Mel Gorman]

As noted by Vlastimil Babka, the migratetype might be wrong if a PCP was
not locked so check the migrate type early. Similarly the !pcp check is
generally unlikely so explicitly tagging it makes sense.

This is a fix for the mm-unstable patch
mm-page_alloc-leave-irqs-enabled-for-per-cpu-page-allocations.patch

Reported-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
---
 mm/page_alloc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 323fec05c4c6..445066617204 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3516,6 +3516,7 @@ void free_unref_page_list(struct list_head *list)
 		struct zone *zone = page_zone(page);
 
 		list_del(&page->lru);
+		migratetype = get_pcppage_migratetype(page);
 
 		/* Different zone, different pcp lock. */
 		if (zone != locked_zone) {
@@ -3530,7 +3531,7 @@ void free_unref_page_list(struct list_head *list)
 			 */
 			pcp_trylock_prepare(UP_flags);
 			pcp = pcp_spin_trylock(zone->per_cpu_pageset);
-			if (!pcp) {
+			if (unlikely(!pcp)) {
 				pcp_trylock_finish(UP_flags);
 				free_one_page(zone, page, page_to_pfn(page),
 					      0, migratetype, FPI_NONE);
@@ -3545,7 +3546,6 @@ void free_unref_page_list(struct list_head *list)
 		 * Non-isolated types over MIGRATE_PCPTYPES get added
 		 * to the MIGRATE_MOVABLE pcp list.
 		 */
-		migratetype = get_pcppage_migratetype(page);
 		if (unlikely(migratetype >= MIGRATE_PCPTYPES))
 			migratetype = MIGRATE_MOVABLE;
 
-- 
2.35.3

[PATCH 2/2] mm/page_alloc: Simplify locking during free_unref_page_list

[Mel Gorman]

While freeing a large list, the zone lock will be released and reacquired
to avoid long hold times since commit c24ad77d962c ("mm/page_alloc.c: avoid
excessive IRQ disabled times in free_unref_page_list()"). As suggested
by Vlastimil Babka, the lockrelease/reacquire logic can be simplified by
reusing the logic that acquires a different lock when changing zones.

Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
---
 mm/page_alloc.c | 25 +++++++++----------------
 1 file changed, 9 insertions(+), 16 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 445066617204..08e32daf0918 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3518,13 +3518,19 @@ void free_unref_page_list(struct list_head *list)
 		list_del(&page->lru);
 		migratetype = get_pcppage_migratetype(page);
 
-		/* Different zone, different pcp lock. */
-		if (zone != locked_zone) {
+		/*
+		 * Either different zone requiring a different pcp lock or
+		 * excessive lock hold times when freeing a large list of
+		 * pages.
+		 */
+		if (zone != locked_zone || batch_count == SWAP_CLUSTER_MAX) {
 			if (pcp) {
 				pcp_spin_unlock(pcp);
 				pcp_trylock_finish(UP_flags);
 			}
 
+			batch_count = 0;
+
 			/*
 			 * trylock is necessary as pages may be getting freed
 			 * from IRQ or SoftIRQ context after an IO completion.
@@ -3539,7 +3545,6 @@ void free_unref_page_list(struct list_head *list)
 				continue;
 			}
 			locked_zone = zone;
-			batch_count = 0;
 		}
 
 		/*
@@ -3551,19 +3556,7 @@ void free_unref_page_list(struct list_head *list)
 
 		trace_mm_page_free_batched(page);
 		free_unref_page_commit(zone, pcp, page, migratetype, 0);
-
-		/*
-		 * Guard against excessive lock hold times when freeing
-		 * a large list of pages. Lock will be reacquired if
-		 * necessary on the next iteration.
-		 */
-		if (++batch_count == SWAP_CLUSTER_MAX) {
-			pcp_spin_unlock(pcp);
-			pcp_trylock_finish(UP_flags);
-			batch_count = 0;
-			pcp = NULL;
-			locked_zone = NULL;
-		}
+		batch_count++;
 	}
 
 	if (pcp) {
-- 
2.35.3