linux-kernel - [PATCH 1/2] mm: add cond_resched to generic_swapfile

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Date:	Fri, 22 Jul 2016 17:11:20 -0400 (EDT)
From:	Mikulas Patocka <mpatocka@...hat.com>
To:	Michal Hocko <mhocko@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Mel Gorman <mgorman@...e.de>,
	Johannes Weiner <hannes@...xchg.org>
cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] mm: add cond_resched to generic_swapfile_activate

The function 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.

Signed-off-by: Mikulas Patocka <mpatocka@...hat.com>

---
 mm/page_io.c |    2 ++
 1 file changed, 2 insertions(+)

Index: linux-4.7-rc7/mm/page_io.c
===================================================================
--- linux-4.7-rc7.orig/mm/page_io.c	2016-05-30 17:34:37.000000000 +0200
+++ linux-4.7-rc7/mm/page_io.c	2016-07-11 17:23:33.000000000 +0200
@@ -166,6 +166,8 @@ int generic_swapfile_activate(struct swa
 		unsigned block_in_page;
 		sector_t first_block;
 
+		cond_resched();
+
 		first_block = bmap(inode, probe_block);
 		if (first_block == 0)
 			goto bad_bmap;