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* [PATCH v2] mm: thp: update split_queue_len correctly
@ 2021-11-23 19:09 Shakeel Butt
  2021-11-23 20:00 ` Yang Shi
  2021-11-24 20:12 ` Kirill A. Shutemov
  0 siblings, 2 replies; 6+ messages in thread
From: Shakeel Butt @ 2021-11-23 19:09 UTC (permalink / raw)
  To: David Hildenbrand, Kirill A . Shutemov, Yang Shi, Zi Yan, Matthew Wilcox
  Cc: Andrew Morton, linux-mm, linux-kernel, Shakeel Butt

The deferred THPs are split on memory pressure through shrinker
callback and splitting of THP during reclaim can fail for several
reasons like unable to lock the THP, under writeback or unexpected
number of pins on the THP. Such pages are put back on the deferred split
list for consideration later. However kernel does not update the
deferred queue size on putting back the pages whose split was failed.
This patch fixes that.

Without this patch the split_queue_len can underflow. Shrinker will
always get that there are some THPs to split even if there are not and
waste some cpu to scan the empty list.

Fixes: 364c1eebe453 ("mm: thp: extract split_queue_* into a struct")
Signed-off-by: Shakeel Butt <shakeelb@google.com>
---
Changes since v1:
- updated commit message
- incorporated Yang Shi's suggestion

 mm/huge_memory.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index e5483347291c..d393028681e2 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2809,7 +2809,7 @@ static unsigned long deferred_split_scan(struct shrinker *shrink,
 	unsigned long flags;
 	LIST_HEAD(list), *pos, *next;
 	struct page *page;
-	int split = 0;
+	unsigned long split = 0;
 
 #ifdef CONFIG_MEMCG
 	if (sc->memcg)
@@ -2847,6 +2847,7 @@ static unsigned long deferred_split_scan(struct shrinker *shrink,
 
 	spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
 	list_splice_tail(&list, &ds_queue->split_queue);
+	ds_queue->split_queue_len -= split;
 	spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
 
 	/*
-- 
2.34.0.rc2.393.gf8c9666880-goog


^ permalink raw reply	[flat|nested] 6+ messages in thread

end of thread, other threads:[~2021-11-24 21:19 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-11-23 19:09 [PATCH v2] mm: thp: update split_queue_len correctly Shakeel Butt
2021-11-23 20:00 ` Yang Shi
2021-11-24 20:12 ` Kirill A. Shutemov
2021-11-24 20:44   ` Shakeel Butt
2021-11-24 21:17     ` Yang Shi
2021-11-24 21:19       ` Shakeel Butt

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