[3.13.y.z extended stable] Patch "mm: page_alloc: fix zone allocation fairness on UP" has been added to staging queue

[Kamal Mostafa]

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

    mm: page_alloc: fix zone allocation fairness on UP

to the linux-3.13.y-queue branch of the 3.13.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11.9.

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

For more information about the 3.13.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 1a002c9591c2970fcd7c6c3f414a206682838b7b Mon Sep 17 00:00:00 2001
From: Johannes Weiner <hannes at cmpxchg.org>
Date: Thu, 2 Oct 2014 00:00:41 +0000
Subject: mm: page_alloc: fix zone allocation fairness on UP

commit abe5f972912d086c080be4bde67750630b6fb38b upstream.

The zone allocation batches can easily underflow due to higher-order
allocations or spills to remote nodes.  On SMP that's fine, because
underflows are expected from concurrency and dealt with by returning 0.
But on UP, zone_page_state will just return a wrapped unsigned long, which
will get past the <= 0 check and then consider the zone eligible until its
watermarks are hit.

3a025760fc15 ("mm: page_alloc: spill to remote nodes before waking
kswapd") already made the counter-resetting use atomic_long_read() to
accomodate underflows from remote spills, but it didn't go all the way
with it.  Make it clear that these batches are expected to go negative
regardless of concurrency, and use atomic_long_read() everywhere.

Fixes: 81c0a2bb515f ("mm: page_alloc: fair zone allocator policy")
Reported-by: Vlastimil Babka <vbabka at suse.cz>
Reported-by: Leon Romanovsky <leon at leon.nu>
Signed-off-by: Johannes Weiner <hannes at cmpxchg.org>
Acked-by: Mel Gorman <mgorman at suse.de>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
[ kamal: Johannes' 3.12 backport applied to 3.13-stable ]
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 mm/page_alloc.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 9aad4f1..38dca81 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1932,7 +1932,7 @@ zonelist_scan:
 		if (alloc_flags & ALLOC_FAIR) {
 			if (!zone_local(preferred_zone, zone))
 				continue;
-			if (zone_page_state(zone, NR_ALLOC_BATCH) <= 0)
+			if (atomic_long_read(&zone->vm_stat[NR_ALLOC_BATCH]) <= 0)
 				continue;
 		}
 		/*
@@ -5599,9 +5599,8 @@ static void __setup_per_zone_wmarks(void)
 		zone->watermark[WMARK_HIGH] = min_wmark_pages(zone) + (tmp >> 1);

 		__mod_zone_page_state(zone, NR_ALLOC_BATCH,
-				      high_wmark_pages(zone) -
-				      low_wmark_pages(zone) -
-				      zone_page_state(zone, NR_ALLOC_BATCH));
+			high_wmark_pages(zone) - low_wmark_pages(zone) -
+			atomic_long_read(&zone->vm_stat[NR_ALLOC_BATCH]));

 		setup_zone_migrate_reserve(zone);
 		spin_unlock_irqrestore(&zone->lock, flags);
--
1.9.1