#define MAX_PAUSE max(HZ/5, 1)
/*
+ * Try to keep balance_dirty_pages() call intervals higher than this many pages
+ * by raising pause time to max_pause when falls below it.
+ */
+#define DIRTY_POLL_THRESH (128 >> (PAGE_SHIFT - 10))
+
+/*
* Estimate write bandwidth at 200ms intervals.
*/
#define BANDWIDTH_INTERVAL max(HZ/5, 1)
t = min(t, 1 + max_pause / 2);
pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
+ /*
+ * Tiny nr_dirtied_pause is found to hurt I/O performance in the test
+ * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}.
+ * When the 16 consecutive reads are often interrupted by some dirty
+ * throttling pause during the async writes, cfq will go into idles
+ * (deadline is fine). So push nr_dirtied_pause as high as possible
+ * until reaches DIRTY_POLL_THRESH=32 pages.
+ */
+ if (pages < DIRTY_POLL_THRESH) {
+ t = max_pause;
+ pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
+ if (pages > DIRTY_POLL_THRESH) {
+ pages = DIRTY_POLL_THRESH;
+ t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit;
+ }
+ }
+
pause = HZ * pages / (task_ratelimit + 1);
if (pause > max_pause) {
t = max_pause;
/*
* The minimal pause time will normally be half the target pause time.
*/
- return 1 + t / 2;
+ return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t;
}
/*