linux-kernel - [PATCH 4/6] mm/page_alloc: Drain the requested list first during bulk free

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Date:   Thu, 17 Feb 2022 00:22:25 +0000
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Aaron Lu <aaron.lu@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...nel.org>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Mel Gorman <mgorman@...hsingularity.net>
Subject: [PATCH 4/6] mm/page_alloc: Drain the requested list first during bulk free

Prior to the series, pindex 0 (order-0 MIGRATE_UNMOVABLE) was always
skipped first and the precise reason is forgotten. A potential reason may
have been to artificially preserve MIGRATE_UNMOVABLE but there is no reason
why that would be optimal as it depends on the workload. The more likely
reason is that it was less complicated to do a pre-increment instead of
a post-increment in terms of overall code flow. As free_pcppages_bulk()
now typically receives the pindex of the PCP list that exceeded high,
always start draining that list.

Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
---
 mm/page_alloc.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index dfc347a58ea6..635a4e0f70b4 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1463,6 +1463,10 @@ static void free_pcppages_bulk(struct zone *zone, int count,
 	 * below while (list_empty(list)) loop.
 	 */
 	count = min(pcp->count, count);
+
+	/* Ensure requested pindex is drained first. */
+	pindex = pindex - 1;
+
 	while (count > 0) {
 		struct list_head *list;
 		int nr_pages;
-- 
2.31.1