From 7e4411bfe6dd29713f879717b433304a1992526d Mon Sep 17 00:00:00 2001
From: Mikulas Patocka <mpatocka@redhat.com>
Date: Thu, 28 Jul 2016 15:48:47 -0700
Subject: [PATCH] mm: add cond_resched() to generic_swapfile_activate()

generic_swapfile_activate() can take quite long time, it iterates over
all blocks of a file, so add cond_resched to it.  I observed about 1
second stalls when activating a swapfile that was almost unfragmented -
this patch fixes it.

Link: http://lkml.kernel.org/r/alpine.LRH.2.02.1607221710580.4818@file01.intranet.prod.int.rdu2.redhat.com
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 mm/page_io.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/page_io.c b/mm/page_io.c
index dcc5d3769608..fb1fa269d3a0 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -166,6 +166,8 @@ int generic_swapfile_activate(struct swap_info_struct *sis,
 		unsigned block_in_page;
 		sector_t first_block;
 
+		cond_resched();
+
 		first_block = bmap(inode, probe_block);
 		if (first_block == 0)
 			goto bad_bmap;
-- 
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