mm/page_alloc: batch page freeing in decay_pcp_high

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/20251014145011.3427205-3-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: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Michal Hocko <mhocko@suse.com>
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>

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index f057ce5ea7da0ad92ece355cf214e400e4d6b5b6..52480f513ba210d238e57e2b99f17ce916253d4d 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2559,7 +2559,7 @@ static int rmqueue_bulk(struct zone *zone, unsigned int order,
  */
 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, struct per_cpu_pages *pcp)
        }
 
        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;