+ mm-page_alloc-simplify-locking-during-free_unref_page_list.patch added to mm-unstable branch

+ mm-page_alloc-simplify-locking-during-free_unref_page_list.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm/page_alloc: simplify locking during free_unref_page_list
has been added to the -mm mm-unstable branch.  Its filename is
     mm-page_alloc-simplify-locking-during-free_unref_page_list.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-page_alloc-simplify-locking-during-free_unref_page_list.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Mel Gorman <mgorman@techsingularity.net>
Subject: mm/page_alloc: simplify locking during free_unref_page_list
Date: Tue, 22 Nov 2022 13:12:29 +0000

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.

Link: https://lkml.kernel.org/r/20221122131229.5263-3-mgorman@techsingularity.net
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/page_alloc.c |   25 +++++++++----------------
 1 file changed, 9 insertions(+), 16 deletions(-)

--- a/mm/page_alloc.c~mm-page_alloc-simplify-locking-during-free_unref_page_list
+++ a/mm/page_alloc.c
@@ -3540,13 +3540,19 @@ void free_unref_page_list(struct list_he
 		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.
@@ -3561,7 +3567,6 @@ void free_unref_page_list(struct list_he
 				continue;
 			}
 			locked_zone = zone;
-			batch_count = 0;
 		}
 
 		/*
@@ -3573,19 +3578,7 @@ void free_unref_page_list(struct list_he
 
 		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) {
_

Patches currently in -mm which might be from mgorman@techsingularity.net are

mm-page_alloc-always-remove-pages-from-temporary-list.patch
mm-page_alloc-leave-irqs-enabled-for-per-cpu-page-allocations.patch
mm-page_alloc-leave-irqs-enabled-for-per-cpu-page-allocations-fix.patch
mm-page_alloc-simplify-locking-during-free_unref_page_list.patch