Merge branch 'fix/pcm-jiffies-check' into topic/pcm-jiffies-check

1 files changed, 19 insertions, 1 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index e2f26991fff1..fe753ecf2aa5 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2681,6 +2681,7 @@ static void __meminit zone_init_free_lists(struct zone *zone)
 
 static int zone_batchsize(struct zone *zone)
 {
+#ifdef CONFIG_MMU
 	int batch;
 
 	/*
@@ -2706,9 +2707,26 @@ static int zone_batchsize(struct zone *zone)
 	 * of pages of one half of the possible page colors
 	 * and the other with pages of the other colors.
 	 */
-	batch = (1 << (fls(batch + batch/2)-1)) - 1;
+	batch = rounddown_pow_of_two(batch + batch/2) - 1;
 
 	return batch;
+
+#else
+	/* The deferral and batching of frees should be suppressed under NOMMU
+	 * conditions.
+	 *
+	 * The problem is that NOMMU needs to be able to allocate large chunks
+	 * of contiguous memory as there's no hardware page translation to
+	 * assemble apparent contiguous memory from discontiguous pages.
+	 *
+	 * Queueing large contiguous runs of pages for batching, however,
+	 * causes the pages to actually be freed in smaller chunks.  As there
+	 * can be a significant delay between the individual batches being
+	 * recycled, this leads to the once large chunks of space being
+	 * fragmented and becoming unavailable for high-order allocations.
+	 */
+	return 0;
+#endif
 }
 
 static void setup_pageset(struct per_cpu_pageset *p, unsigned long batch)