When adjusting the CONFIG_PCP_BATCH_SCALE_MAX configuration from its
default value of 5 to a lower value, such as 0, it's important to ensure
that the pcp->high decaying is not inadvertently slowed down. Similarly,
when increasing CONFIG_PCP_BATCH_SCALE_MAX to a larger value, like 6, we
must avoid inadvertently increasing the number of pages freed in
free_pcppages_bulk() as a result of this change.
So below improvements are made:
- hardcode the default value of 5 to avoiding modifying the pcp->high
- change free_pcppages_bulk() calling into multiple steps
Suggested-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
---
mm/page_alloc.c | 16 ++++++++++++----
1 file changed, 12 insertions(+), 4 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d9371806f6b5..5a842cc13314 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2323,7 +2323,7 @@ static int rmqueue_bulk(struct zone *zone, unsigned int order,
int decay_pcp_high(struct zone *zone, struct per_cpu_pages *pcp)
{
int high_min, to_drain, batch;
- int todo = 0;
+ int todo = 0, count = 0;
high_min = READ_ONCE(pcp->high_min);
batch = READ_ONCE(pcp->batch);
@@ -2333,18 +2333,26 @@ int decay_pcp_high(struct zone *zone, struct per_cpu_pages *pcp)
* control latency. This caps pcp->high decrement too.
*/
if (pcp->high > high_min) {
- pcp->high = max3(pcp->count - (batch << CONFIG_PCP_BATCH_SCALE_MAX),
+ /*
+ * We will decay 1/8 pcp->high each time in general, so that the
+ * idle PCP pages can be returned to buddy system timely. To
+ * control the max latency of decay, we also constrain the
+ * number pages freed each time.
+ */
+ pcp->high = max3(pcp->count - (batch << 5),
pcp->high - (pcp->high >> 3), high_min);
if (pcp->high > high_min)
todo++;
}
to_drain = pcp->count - pcp->high;
- if (to_drain > 0) {
+ while (count < to_drain) {
spin_lock(&pcp->lock);
- free_pcppages_bulk(zone, to_drain, pcp, 0);
+ free_pcppages_bulk(zone, min(batch, to_drain - count), pcp, 0);
spin_unlock(&pcp->lock);
+ count += batch;
todo++;
+ cond_resched();
}
return todo;
--
2.34.1
