The patch titled
Subject: mm, pcp: decrease PCP high if free pages < high watermark
has been added to the -mm mm-unstable branch. Its filename is
mm-pcp-decrease-pcp-high-if-free-pages-high-watermark.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-pcp-decrease-pcp-high-if-free-pages-high-watermark.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: Huang Ying <ying.huang@xxxxxxxxx>
Subject: mm, pcp: decrease PCP high if free pages < high watermark
Date: Mon, 16 Oct 2023 13:30:01 +0800
One target of PCP is to minimize pages in PCP if the system free pages is
too few. To reach that target, when page reclaiming is active for the
zone (ZONE_RECLAIM_ACTIVE), we will stop increasing PCP high in allocating
path, decrease PCP high and free some pages in freeing path. But this may
be too late because the background page reclaiming may introduce latency
for some workloads. So, in this patch, during page allocation we will
detect whether the number of free pages of the zone is below high
watermark. If so, we will stop increasing PCP high in allocating path,
decrease PCP high and free some pages in freeing path. With this, we can
reduce the possibility of the premature background page reclaiming caused
by too large PCP.
The high watermark checking is done in allocating path to reduce the
overhead in hotter freeing path.
Link: https://lkml.kernel.org/r/20231016053002.756205-9-ying.huang@xxxxxxxxx
Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Johannes Weiner <jweiner@xxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
Cc: Sudeep Holla <sudeep.holla@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/mmzone.h | 1 +
mm/page_alloc.c | 33 +++++++++++++++++++++++++++++++--
2 files changed, 32 insertions(+), 2 deletions(-)
--- a/include/linux/mmzone.h~mm-pcp-decrease-pcp-high-if-free-pages-high-watermark
+++ a/include/linux/mmzone.h
@@ -1030,6 +1030,7 @@ enum zone_flags {
* Cleared when kswapd is woken.
*/
ZONE_RECLAIM_ACTIVE, /* kswapd may be scanning the zone. */
+ ZONE_BELOW_HIGH, /* zone is below high watermark. */
};
static inline unsigned long zone_managed_pages(struct zone *zone)
--- a/mm/page_alloc.c~mm-pcp-decrease-pcp-high-if-free-pages-high-watermark
+++ a/mm/page_alloc.c
@@ -2443,7 +2443,13 @@ static int nr_pcp_high(struct per_cpu_pa
return min(batch << 2, pcp->high);
}
- if (pcp->count >= high && high_min != high_max) {
+ if (high_min == high_max)
+ return high;
+
+ if (test_bit(ZONE_BELOW_HIGH, &zone->flags)) {
+ pcp->high = max(high - (batch << pcp->free_factor), high_min);
+ high = max(pcp->count, high_min);
+ } else if (pcp->count >= high) {
int need_high = (batch << pcp->free_factor) + batch;
/* pcp->high should be large enough to hold batch freed pages */
@@ -2493,6 +2499,10 @@ static void free_unref_page_commit(struc
if (pcp->count >= high) {
free_pcppages_bulk(zone, nr_pcp_free(pcp, batch, high, free_high),
pcp, pindex);
+ if (test_bit(ZONE_BELOW_HIGH, &zone->flags) &&
+ zone_watermark_ok(zone, 0, high_wmark_pages(zone),
+ ZONE_MOVABLE, 0))
+ clear_bit(ZONE_BELOW_HIGH, &zone->flags);
}
}
@@ -2799,7 +2809,7 @@ static int nr_pcp_alloc(struct per_cpu_p
* If we had larger pcp->high, we could avoid to allocate from
* zone.
*/
- if (high_min != high_max && !test_bit(ZONE_RECLAIM_ACTIVE, &zone->flags))
+ if (high_min != high_max && !test_bit(ZONE_BELOW_HIGH, &zone->flags))
high = pcp->high = min(high + batch, high_max);
if (!order) {
@@ -3261,6 +3271,25 @@ retry:
}
}
+ /*
+ * Detect whether the number of free pages is below high
+ * watermark. If so, we will decrease pcp->high and free
+ * PCP pages in free path to reduce the possibility of
+ * premature page reclaiming. Detection is done here to
+ * avoid to do that in hotter free path.
+ */
+ if (test_bit(ZONE_BELOW_HIGH, &zone->flags))
+ goto check_alloc_wmark;
+
+ mark = high_wmark_pages(zone);
+ if (zone_watermark_fast(zone, order, mark,
+ ac->highest_zoneidx, alloc_flags,
+ gfp_mask))
+ goto try_this_zone;
+ else
+ set_bit(ZONE_BELOW_HIGH, &zone->flags);
+
+check_alloc_wmark:
mark = wmark_pages(zone, alloc_flags & ALLOC_WMARK_MASK);
if (!zone_watermark_fast(zone, order, mark,
ac->highest_zoneidx, alloc_flags,
_
Patches currently in -mm which might be from ying.huang@xxxxxxxxx are
mm-fix-draining-remote-pageset.patch
mm-pcp-avoid-to-drain-pcp-when-process-exit.patch
cacheinfo-calculate-size-of-per-cpu-data-cache-slice.patch
mm-pcp-reduce-lock-contention-for-draining-high-order-pages.patch
mm-restrict-the-pcp-batch-scale-factor-to-avoid-too-long-latency.patch
mm-page_alloc-scale-the-number-of-pages-that-are-batch-allocated.patch
mm-add-framework-for-pcp-high-auto-tuning.patch
mm-tune-pcp-high-automatically.patch
mm-pcp-decrease-pcp-high-if-free-pages-high-watermark.patch
mm-pcp-reduce-detecting-time-of-consecutive-high-order-page-freeing.patch
