--- mm/vmscan.c

+++ mm/vmscan.c

@@ -1083,6 +1083,48 @@ static int too_many_isolated(struct zone

}

/*

+ * Returns true if the caller should wait to clean dirty/writeback pages.

+ *

+ * If we are direct reclaiming for contiguous pages and we do not reclaim

+ * everything in the list, try again and wait for writeback IO to complete.

+ * This will stall high-order allocations noticeably. Only do that when really

+ * need to free the pages under high memory pressure.

+ */

+static inline bool should_reclaim_stall(unsigned long nr_taken,

+ unsigned long nr_freed,

+ int priority,

+ int lumpy_reclaim,

+ struct scan_control *sc)

+{

+ int lumpy_stall_priority;

+

+ /* kswapd should not stall on sync IO */

+ if (current_is_kswapd())

+ return false;

+

+ /* Only stall on lumpy reclaim */

+ if (!lumpy_reclaim)

+ return false;

+

+ /* If we have relaimed everything on the isolated list, no stall */

+ if (nr_freed == nr_taken)

+ return false;

+

+ /*

+ * For high-order allocations, there are two stall thresholds.

+ * High-cost allocations stall immediately where as lower

+ * order allocations such as stacks require the scanning

+ * priority to be much higher before stalling.

+ */

+ if (sc->order > PAGE_ALLOC_COSTLY_ORDER)

+ lumpy_stall_priority = DEF_PRIORITY;

+ else

+ lumpy_stall_priority = DEF_PRIORITY / 3;

+

+ return priority <= lumpy_stall_priority;

+}

+

+/*

* shrink_inactive_list() is a helper for shrink_zone(). It returns the number

* of reclaimed pages

*/

@@ -1176,14 +1218,9 @@ static unsigned long shrink_inactive_lis

nr_scanned += nr_scan;

nr_freed = shrink_page_list(&page_list, sc, PAGEOUT_IO_ASYNC);

- /*

- * If we are direct reclaiming for contiguous pages and we do

- * not reclaim everything in the list, try again and wait

- * for IO to complete. This will stall high-order allocations

- * but that should be acceptable to the caller

- */

- if (nr_freed < nr_taken && !current_is_kswapd() &&

- lumpy_reclaim) {

+ /* Check if we should syncronously wait for writeback */

+ if (should_reclaim_stall(nr_taken, nr_freed, priority,

+ lumpy_reclaim, sc)) {

congestion_wait(BLK_RW_ASYNC, HZ/10);

/*