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* [PATCH] mm: page_alloc: avoid excessive IRQ disabled times in free_unref_page_list
@ 2017-12-07 17:03 Lucas Stach
  2017-12-07 19:51 ` Mel Gorman
  0 siblings, 1 reply; 8+ messages in thread
From: Lucas Stach @ 2017-12-07 17:03 UTC (permalink / raw)
  To: Andrew Morton, Mel Gorman
  Cc: Michal Hocko, Vlastimil Babka, linux-mm, kernel, patchwork-lst

Since 9cca35d42eb6 (mm, page_alloc: enable/disable IRQs once when freeing
a list of pages) we see excessive IRQ disabled times of up to 250ms on an
embedded ARM system (tracing overhead included).

This is due to graphics buffers being freed back to the system via
release_pages(). Graphics buffers can be huge, so it's not hard to hit
cases where the list of pages to free has 2048 entries. Disabling IRQs
while freeing all those pages is clearly not a good idea.

Introduce a batch limit, which allows IRQ servicing once every few pages.
The batch count is the same as used in other parts of the MM subsystem
when dealing with IRQ disabled regions.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
---
 mm/page_alloc.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 73f5d4556b3d..7e5e775e97f4 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2684,6 +2684,7 @@ void free_unref_page_list(struct list_head *list)
 {
 	struct page *page, *next;
 	unsigned long flags, pfn;
+	int batch_count = 0;
 
 	/* Prepare pages for freeing */
 	list_for_each_entry_safe(page, next, list, lru) {
@@ -2700,6 +2701,16 @@ void free_unref_page_list(struct list_head *list)
 		set_page_private(page, 0);
 		trace_mm_page_free_batched(page);
 		free_unref_page_commit(page, pfn);
+
+		/*
+		 * Guard against excessive IRQ disabled times when we get
+		 * a large list of pages to free.
+		 */
+		if (++batch_count == SWAP_CLUSTER_MAX) {
+			local_irq_restore(flags);
+			batch_count = 0;
+			local_irq_save(flags);
+		}
 	}
 	local_irq_restore(flags);
 }
-- 
2.11.0

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^ permalink raw reply related	[flat|nested] 8+ messages in thread

end of thread, other threads:[~2017-12-08 11:39 UTC | newest]

Thread overview: 8+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2017-12-07 17:03 [PATCH] mm: page_alloc: avoid excessive IRQ disabled times in free_unref_page_list Lucas Stach
2017-12-07 19:51 ` Mel Gorman
2017-12-07 23:20   ` Andrew Morton
2017-12-08  0:25     ` Mel Gorman
2017-12-08  0:53       ` Andrew Morton
2017-12-08 10:21         ` Mel Gorman
2017-12-08 10:03   ` Lucas Stach
2017-12-08 11:38     ` Mel Gorman

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