This is a note to let you know that I've just added the patch titled

mm/compaction: fix invalid free_pfn and compact_cached_free_pfn

to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: mm-compaction-fix-invalid-free_pfn-and-compact_cached_free_pfn.patch and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From 623446e4dc45b37740268165107cc63abb3022f0 Mon Sep 17 00:00:00 2001

From: Joonsoo Kim iamjoonsoo.kim@lge.com Date: Tue, 15 Mar 2016 14:57:45 -0700 Subject: mm/compaction: fix invalid free_pfn and compact_cached_free_pfn

From: Joonsoo Kim iamjoonsoo.kim@lge.com

commit 623446e4dc45b37740268165107cc63abb3022f0 upstream.

free_pfn and compact_cached_free_pfn are the pointer that remember restart position of freepage scanner. When they are reset or invalid, we set them to zone_end_pfn because freepage scanner works in reverse direction. But, because zone range is defined as [zone_start_pfn, zone_end_pfn), zone_end_pfn is invalid to access. Therefore, we should not store it to free_pfn and compact_cached_free_pfn. Instead, we need to store zone_end_pfn - 1 to them. There is one more thing we should consider. Freepage scanner scan reversely by pageblock unit. If free_pfn and compact_cached_free_pfn are set to middle of pageblock, it regards that sitiation as that it already scans front part of pageblock so we lose opportunity to scan there. To fix-up, this patch do round_down() to guarantee that reset position will be pageblock aligned.

Note that thanks to the current pageblock_pfn_to_page() implementation, actual access to zone_end_pfn doesn't happen until now. But, following patch will change pageblock_pfn_to_page() so this patch is needed from now on.

Signed-off-by: Joonsoo Kim iamjoonsoo.kim@lge.com Acked-by: David Rientjes rientjes@google.com Acked-by: Vlastimil Babka vbabka@suse.cz Cc: Aaron Lu aaron.lu@intel.com Cc: Mel Gorman mgorman@suse.de Cc: Rik van Riel riel@redhat.com 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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

--- mm/compaction.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)

--- a/mm/compaction.c +++ b/mm/compaction.c @@ -200,7 +200,8 @@ static void reset_cached_positions(struc { zone->compact_cached_migrate_pfn[0] = zone->zone_start_pfn; zone->compact_cached_migrate_pfn[1] = zone->zone_start_pfn; - zone->compact_cached_free_pfn = zone_end_pfn(zone); + zone->compact_cached_free_pfn = + round_down(zone_end_pfn(zone) - 1, pageblock_nr_pages); }

/* @@ -1358,11 +1359,11 @@ static int compact_zone(struct zone *zon */ cc->migrate_pfn = zone->compact_cached_migrate_pfn[sync]; cc->free_pfn = zone->compact_cached_free_pfn; - if (cc->free_pfn < start_pfn || cc->free_pfn > end_pfn) { - cc->free_pfn = end_pfn & ~(pageblock_nr_pages-1); + if (cc->free_pfn < start_pfn || cc->free_pfn >= end_pfn) { + cc->free_pfn = round_down(end_pfn - 1, pageblock_nr_pages); zone->compact_cached_free_pfn = cc->free_pfn; } - if (cc->migrate_pfn < start_pfn || cc->migrate_pfn > end_pfn) { + if (cc->migrate_pfn < start_pfn || cc->migrate_pfn >= end_pfn) { cc->migrate_pfn = start_pfn; zone->compact_cached_migrate_pfn[0] = cc->migrate_pfn; zone->compact_cached_migrate_pfn[1] = cc->migrate_pfn;

Patches currently in stable-queue which might be from iamjoonsoo.kim@lge.com are

queue-4.4/mm-compaction-pass-only-pageblock-aligned-range-to-pageblock_pfn_to_page.patch queue-4.4/mm-compaction-fix-invalid-free_pfn-and-compact_cached_free_pfn.patch