The patch titled
Subject: mm, page_alloc: reserve pageblocks for high-order atomic allocations on demand -fix
has been added to the -mm tree. Its filename is
mm-page_alloc-reserve-pageblocks-for-high-order-atomic-allocations-on-demand-fix.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-page_alloc-reserve-pageblocks-for-high-order-atomic-allocations-on-demand-fix.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-page_alloc-reserve-pageblocks-for-high-order-atomic-allocations-on-demand-fix.patch
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------------------------------------------------------
From: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Subject: mm, page_alloc: reserve pageblocks for high-order atomic allocations on demand -fix
nr_reserved_highatomic is checked outside the zone lock so there is a race
whereby the reserve is larger than the limit allows. This patch rechecks
the count under the zone lock.
During unreserving, there is a possibility we could underflow if there
ever was a race between per-cpu drains, reserve and unreserving. This
patch adds a comment about the potential race and protects against it.
These are two fixes to the mmotm patch
mm-page_alloc-reserve-pageblocks-for-high-order-atomic-allocations-on-demand.patch
. They are not separate patches and they should all be folded together.
Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Vitaly Wool <vitalywool@xxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 17 +++++++++++++++--
1 file changed, 15 insertions(+), 2 deletions(-)
diff -puN mm/page_alloc.c~mm-page_alloc-reserve-pageblocks-for-high-order-atomic-allocations-on-demand-fix mm/page_alloc.c
--- a/mm/page_alloc.c~mm-page_alloc-reserve-pageblocks-for-high-order-atomic-allocations-on-demand-fix
+++ a/mm/page_alloc.c
@@ -1633,9 +1633,13 @@ static void reserve_highatomic_pageblock
if (zone->nr_reserved_highatomic >= max_managed)
return;
- /* Yoink! */
spin_lock_irqsave(&zone->lock, flags);
+ /* Recheck the nr_reserved_highatomic limit under the lock */
+ if (zone->nr_reserved_highatomic >= max_managed)
+ goto out_unlock;
+
+ /* Yoink! */
mt = get_pageblock_migratetype(page);
if (mt != MIGRATE_HIGHATOMIC &&
!is_migrate_isolate(mt) && !is_migrate_cma(mt)) {
@@ -1643,6 +1647,8 @@ static void reserve_highatomic_pageblock
set_pageblock_migratetype(page, MIGRATE_HIGHATOMIC);
move_freepages_block(zone, page, MIGRATE_HIGHATOMIC);
}
+
+out_unlock:
spin_unlock_irqrestore(&zone->lock, flags);
}
@@ -1677,7 +1683,14 @@ static void unreserve_highatomic_pageblo
page = list_entry(area->free_list[MIGRATE_HIGHATOMIC].next,
struct page, lru);
- zone->nr_reserved_highatomic -= pageblock_nr_pages;
+ /*
+ * It should never happen but changes to locking could
+ * inadvertently allow a per-cpu drain to add pages
+ * to MIGRATE_HIGHATOMIC while unreserving so be safe
+ * and watch for underflows.
+ */
+ zone->nr_reserved_highatomic -= min(pageblock_nr_pages,
+ zone->nr_reserved_highatomic);
/*
* Convert to ac->migratetype and avoid the normal
_
Patches currently in -mm which might be from mgorman@xxxxxxxxxxxxxxxxxxx are
mm-hugetlbfs-skip-shared-vmas-when-unmapping-private-pages-to-satisfy-a-fault.patch
mm-page_alloc-remove-unnecessary-parameter-from-zone_watermark_ok_safe.patch
mm-page_alloc-remove-unnecessary-recalculations-for-dirty-zone-balancing.patch
mm-page_alloc-remove-unnecessary-taking-of-a-seqlock-when-cpusets-are-disabled.patch
mm-page_alloc-use-masks-and-shifts-when-converting-gfp-flags-to-migrate-types.patch
mm-page_alloc-distinguish-between-being-unable-to-sleep-unwilling-to-sleep-and-avoiding-waking-kswapd.patch
mm-page_alloc-rename-__gfp_wait-to-__gfp_reclaim.patch
mm-page_alloc-delete-the-zonelist_cache.patch
mm-page_alloc-remove-migrate_reserve.patch
mm-page_alloc-reserve-pageblocks-for-high-order-atomic-allocations-on-demand.patch
mm-page_alloc-reserve-pageblocks-for-high-order-atomic-allocations-on-demand-fix.patch
mm-page_alloc-only-enforce-watermarks-for-order-0-allocations.patch
mm-page_alloc-only-enforce-watermarks-for-order-0-allocations-fix.patch
mm-page_alloc-hide-some-GFP-internals-and-document-the-bit-and-flag-combinations.patch
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