From b22ee1fc781430a04597ab531680f2d6111eef94 Mon Sep 17 00:00:00 2001
From: Johannes Weiner <hannes@cmpxchg.org>
Date: Mon, 14 Dec 2020 19:12:15 -0800
Subject: [PATCH] mm: don't wake kswapd prematurely when watermark boosting is
disabled
References: git fixes (mm/vmscan)
Patch-mainline: v5.11
Git-commit: 597c892038e08098b17ccfe65afd9677e6979800
On 2-node NUMA hosts we see bursts of kswapd reclaim and subsequent
pressure spikes and stalls from cache refaults while there is plenty of
free memory in the system.
Usually, kswapd is woken up when all eligible nodes in an allocation are
full. But the code related to watermark boosting can wake kswapd on one
full node while the other one is mostly empty. This may be justified to
fight fragmentation, but is currently unconditionally done whether
watermark boosting is occurring or not.
In our case, many of our workloads' throughput scales with available
memory, and pure utilization is a more tangible concern than trends
around longer-term fragmentation. As a result we generally disable
watermark boosting.
Wake kswapd only woken when watermark boosting is requested.
Link: https://lkml.kernel.org/r/20201020175833.397286-1-hannes@cmpxchg.org
Fixes: 1c30844d2dfe ("mm: reclaim small amounts of memory when an external fragmentation event occurs")
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Mel Gorman <mgorman@suse.de>
---
mm/page_alloc.c | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 9ff3ff6da860..ec2be0b637d1 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2020,12 +2020,12 @@ static bool can_steal_fallback(unsigned int order, int start_mt)
return false;
}
-static inline void boost_watermark(struct zone *zone)
+static inline bool boost_watermark(struct zone *zone)
{
unsigned long max_boost;
if (!watermark_boost_factor)
- return;
+ return false;
/*
* Don't bother in zones that are unlikely to produce results.
* On small machines, including kdump capture kernels running
@@ -2033,7 +2033,7 @@ static inline void boost_watermark(struct zone *zone)
* memory situation immediately.
*/
if ((pageblock_nr_pages * 4) > zone->managed_pages)
- return;
+ return false;
max_boost = mult_frac(zone->_watermark[WMARK_HIGH],
watermark_boost_factor, 10000);
@@ -2047,12 +2047,14 @@ static inline void boost_watermark(struct zone *zone)
* boosted watermark resulting in a hang.
*/
if (!max_boost)
- return;
+ return false;
max_boost = max(pageblock_nr_pages, max_boost);
zone->watermark_boost = min(zone->watermark_boost + pageblock_nr_pages,
max_boost);
+
+ return true;
}
/*
@@ -2091,8 +2093,7 @@ static void steal_suitable_fallback(struct zone *zone, struct page *page,
* likelihood of future fallbacks. Wake kswapd now as the node
* may be balanced overall and kswapd will not wake naturally.
*/
- boost_watermark(zone);
- if (alloc_flags & ALLOC_KSWAPD)
+ if (boost_watermark(zone) && (alloc_flags & ALLOC_KSWAPD))
set_bit(ZONE_BOOSTED_WATERMARK, &zone->flags);
/* We are not allowed to try stealing from the whole block */