+ mm-page_alloc-batch-page-freeing-in-decay_pcp_high.patch added to mm-new branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/page_alloc: batch page freeing in decay_pcp_high
has been added to the -mm mm-new branch.  Its filename is
     mm-page_alloc-batch-page-freeing-in-decay_pcp_high.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-batch-page-freeing-in-decay_pcp_high.patch

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

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
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------------------------------------------------------
From: Joshua Hahn <joshua.hahnjy@gmail.com>
Subject: mm/page_alloc: batch page freeing in decay_pcp_high
Date: Mon, 13 Oct 2025 12:08:10 -0700

It is possible for pcp->count - pcp->high to exceed pcp->batch by a lot. 
When this happens, we should perform batching to ensure that
free_pcppages_bulk isn't called with too many pages to free at once and
starve out other threads that need the pcp or zone lock.

Since we are still only freeing the difference between the initial
pcp->count and pcp->high values, there should be no change to how many
pages are freed.

Link: https://lkml.kernel.org/r/20251013190812.787205-3-joshua.hahnjy@gmail.com
Signed-off-by: Joshua Hahn <joshua.hahnjy@gmail.com>
Suggested-by: Chris Mason <clm@fb.com>
Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Co-developed-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: SeongJae Park <sj@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/page_alloc.c |    9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

--- a/mm/page_alloc.c~mm-page_alloc-batch-page-freeing-in-decay_pcp_high
+++ a/mm/page_alloc.c
@@ -2559,7 +2559,7 @@ static int rmqueue_bulk(struct zone *zon
  */
 bool decay_pcp_high(struct zone *zone, struct per_cpu_pages *pcp)
 {
-	int high_min, to_drain, batch;
+	int high_min, to_drain, to_drain_batched, batch;
 	bool todo = false;
 
 	high_min = READ_ONCE(pcp->high_min);
@@ -2577,11 +2577,14 @@ bool decay_pcp_high(struct zone *zone, s
 	}
 
 	to_drain = pcp->count - pcp->high;
-	if (to_drain > 0) {
+	while (to_drain > 0) {
+		to_drain_batched = min(to_drain, batch);
 		spin_lock(&pcp->lock);
-		free_pcppages_bulk(zone, to_drain, pcp, 0);
+		free_pcppages_bulk(zone, to_drain_batched, pcp, 0);
 		spin_unlock(&pcp->lock);
 		todo = true;
+
+		to_drain -= to_drain_batched;
 	}
 
 	return todo;
_

Patches currently in -mm which might be from joshua.hahnjy@gmail.com are

mm-page_alloc-clarify-batch-tuning-in-zone_batchsize.patch
mm-page_alloc-prevent-reporting-pcp-batch-=-0.patch
mm-page_alloc-vmstat-simplify-refresh_cpu_vm_stats-change-detection.patch
mm-page_alloc-batch-page-freeing-in-decay_pcp_high.patch
mm-page_alloc-batch-page-freeing-in-free_frozen_page_commit.patch