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

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Date:   Tue, 22 Nov 2022 13:12:28 +0000
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Hugh Dickins <hughd@...gle.com>, Yu Zhao <yuzhao@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        Michal Hocko <mhocko@...nel.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Mel Gorman <mgorman@...hsingularity.net>
Subject: [PATCH 1/2] mm/page_alloc: Leave IRQs enabled for per-cpu page allocations -fix

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@...e.cz>
Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
Acked-by: Vlastimil Babka <vbabka@...e.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