From 077b9a7f9643e49928ecc3fbb71b0ee49403e8a6 Mon Sep 17 00:00:00 2001
From: Lucas Stach <l.stach@pengutronix.de>
Date: Thu, 14 Dec 2017 15:32:55 -0800
Subject: [PATCH] mm/page_alloc.c: avoid excessive IRQ disabled times in
 free_unref_page_list()

References: bnc#971975 VM -- git fixes
Patch-mainline: v4.15-rc4
Git-commit: c24ad77d962c31af92f2b731dad2104cbf3fbb03

Since commit 9cca35d42eb6 ("mm, page_alloc: enable/disable IRQs once
when freeing a list of pages") we see excessive IRQ disabled times of up
to 25ms 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.

Link: http://lkml.kernel.org/r/20171207170314.4419-1-l.stach@pengutronix.de
Fixes: 9cca35d42eb6 ("mm, page_alloc: enable/disable IRQs once when freeing a list of pages")
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Acked-by: Mel Gorman <mgorman@suse.de>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
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 | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 81734d260683..ab95865407ed 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2622,6 +2622,7 @@ 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) {
@@ -2638,6 +2639,16 @@ 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);
 }