1 files changed, 29 insertions, 0 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 2cb9eb71e282..4f95bcf0f2b1 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1735,6 +1735,35 @@ zonelist_scan:
                 if ((alloc_flags & ALLOC_CPUSET) &&
                         !cpuset_zone_allowed_softwall(zone, gfp_mask))
                                 continue;
+                /*
+                 * When allocating a page cache page for writing, we
+                 * want to get it from a zone that is within its dirty
+                 * limit, such that no single zone holds more than its
+                 * proportional share of globally allowed dirty pages.
+                 * The dirty limits take into account the zone's
+                 * lowmem reserves and high watermark so that kswapd
+                 * should be able to balance it without having to
+                 * write pages from its LRU list.
+                 *
+                 * This may look like it could increase pressure on
+                 * lower zones by failing allocations in higher zones
+                 * before they are full.  But the pages that do spill
+                 * over are limited as the lower zones are protected
+                 * by this very same mechanism.  It should not become
+                 * a practical burden to them.
+                 *
+                 * XXX: For now, allow allocations to potentially
+                 * exceed the per-zone dirty limit in the slowpath
+                 * (ALLOC_WMARK_LOW unset) before going into reclaim,
+                 * which is important when on a NUMA setup the allowed
+                 * zones are together not big enough to reach the
+                 * global limit.  The proper fix for these situations
+                 * will require awareness of zones in the
+                 * dirty-throttling and the flusher threads.
+                 */
+                if ((alloc_flags & ALLOC_WMARK_LOW) &&
+                    (gfp_mask & __GFP_WRITE) && !zone_dirty_ok(zone))
+                        goto this_zone_full;
 
                 BUILD_BUG_ON(ALLOC_NO_WATERMARKS < NR_WMARK);
                 if (!(alloc_flags & ALLOC_NO_WATERMARKS)) {