mm: page_alloc: generalize the dirty balance reserve

The dirty balance reserve that dirty throttling has to consider is
merely memory not available to userspace allocations.  There is nothing
writeback-specific about it.  Generalize the name so that it's reusable
outside of that context.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 12 insertions, 2 deletions

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index d15d88c..6fe7d15 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -278,7 +278,12 @@ static unsigned long zone_dirtyable_memory(struct zone *zone)
 	unsigned long nr_pages;
 
 	nr_pages = zone_page_state(zone, NR_FREE_PAGES);
-	nr_pages -= min(nr_pages, zone->dirty_balance_reserve);
+	/*
+	 * Pages reserved for the kernel should not be considered
+	 * dirtyable, to prevent a situation where reclaim has to
+	 * clean pages in order to balance the zones.
+	 */
+	nr_pages -= min(nr_pages, zone->totalreserve_pages);
 
 	nr_pages += zone_page_state(zone, NR_INACTIVE_FILE);
 	nr_pages += zone_page_state(zone, NR_ACTIVE_FILE);
@@ -332,7 +337,12 @@ static unsigned long global_dirtyable_memory(void)
 	unsigned long x;
 
 	x = global_page_state(NR_FREE_PAGES);
-	x -= min(x, dirty_balance_reserve);
+	/*
+	 * Pages reserved for the kernel should not be considered
+	 * dirtyable, to prevent a situation where reclaim has to
+	 * clean pages in order to balance the zones.
+	 */
+	x -= min(x, totalreserve_pages);
 
 	x += global_page_state(NR_INACTIVE_FILE);
 	x += global_page_state(NR_ACTIVE_FILE);