page_alloc: fix invalid watermark check on a negative value

[sfrench/cifs-2.6.git] / mm / page_alloc.c

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index e008a3df0485c79ac24ef31b4407dd5921a9649a..b5b14b78c4fd4844cb071022570fd4b7e6959eb2 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3968,11 +3968,15 @@ static inline bool zone_watermark_fast(struct zone *z, unsigned int order,
         * need to be calculated.
         */
        if (!order) {
-               long fast_free;
+               long usable_free;
+               long reserved;
 
-               fast_free = free_pages;
-               fast_free -= __zone_watermark_unusable_free(z, 0, alloc_flags);
-               if (fast_free > mark + z->lowmem_reserve[highest_zoneidx])
+               usable_free = free_pages;
+               reserved = __zone_watermark_unusable_free(z, 0, alloc_flags);
+
+               /* reserved may over estimate high-atomic reserves. */
+               usable_free -= min(usable_free, reserved);
+               if (usable_free > mark + z->lowmem_reserve[highest_zoneidx])
                        return true;
        }