[4.2.y-ckt stable] Patch "mm, cma: prevent nr_isolated_* counters from going negative" has been added to the 4.2.y-ckt tree

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    mm, cma: prevent nr_isolated_* counters from going negative

to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
which can be found at:

    https://git.launchpad.net/~canonical-kernel/linux/+git/linux-stable-ckt/log/?h=linux-4.2.y-queue

This patch is scheduled to be released in version 4.2.8-ckt10.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From b33d8d45dc9bcc241ca403d26e747f8dcf251d3d Mon Sep 17 00:00:00 2001
From: Hugh Dickins <hughd at google.com>
Date: Thu, 5 May 2016 16:22:15 -0700
Subject: mm, cma: prevent nr_isolated_* counters from going negative

commit 14af4a5e9b26ad251f81c174e8a43f3e179434a5 upstream.

/proc/sys/vm/stat_refresh warns nr_isolated_anon and nr_isolated_file go
increasingly negative under compaction: which would add delay when
should be none, or no delay when should delay.  The bug in compaction
was due to a recent mmotm patch, but much older instance of the bug was
also noticed in isolate_migratepages_range() which is used for CMA and
gigantic hugepage allocations.

The bug is caused by putback_movable_pages() in an error path
decrementing the isolated counters without them being previously
incremented by acct_isolated().  Fix isolate_migratepages_range() by
removing the error-path putback, thus reaching acct_isolated() with
migratepages still isolated, and leaving putback to caller like most
other places do.

Fixes: edc2ca612496 ("mm, compaction: move pageblock checks up from isolate_migratepages_range()")
[vbabka at suse.cz: expanded the changelog]
Signed-off-by: Hugh Dickins <hughd at google.com>
Signed-off-by: Vlastimil Babka <vbabka at suse.cz>
Acked-by: Joonsoo Kim <iamjoonsoo.kim at lge.com>
Cc: Michal Hocko <mhocko at kernel.org>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 mm/compaction.c | 10 +---------
 1 file changed, 1 insertion(+), 9 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index 018f08d..3dcf93c 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -853,16 +853,8 @@ isolate_migratepages_range(struct compact_control *cc, unsigned long start_pfn,
 		pfn = isolate_migratepages_block(cc, pfn, block_end_pfn,
 							ISOLATE_UNEVICTABLE);

-		/*
-		 * In case of fatal failure, release everything that might
-		 * have been isolated in the previous iteration, and signal
-		 * the failure back to caller.
-		 */
-		if (!pfn) {
-			putback_movable_pages(&cc->migratepages);
-			cc->nr_migratepages = 0;
+		if (!pfn)
 			break;
-		}

 		if (cc->nr_migratepages == COMPACT_CLUSTER_MAX)
 			break;
--
2.7.4