[PATCH 3/6] blk-cgroup: buffered write IO controller - bandwidth weight

[Fengguang Wu <fengguang.wu@intel.com>]

[-- Attachment #1: writeback-io-controller-weight.patch --]
[-- Type: text/plain, Size: 3526 bytes --]

blkcg->weight can be trivially supported for buffered writes by directly
scaling task_ratelimit in balance_dirty_pages().

However the sementics are not quite the same with direct IO.

- for direct IO, weight is normally applied to disk time
- for buffered writes, weight is applied to dirty rate

Notes about the (balanced_dirty_ratelimit > write_bw) check removal:

When there is only one dd running and its weight is set to
BLKIO_WEIGHT_MIN=10, bdi->dirty_ratelimit will end up balancing around

	write_bw * BLKIO_WEIGHT_DEFAULT / BLKIO_WEIGHT_MIN 
	= write_bw * 50

So the limit should now be raised to (write_bw * 50) to deal with the
above extreme case, which seems too large to be useful for normal cases.
So just remove it.

Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
---
 include/linux/blk-cgroup.h |   18 ++++++++++++++----
 mm/page-writeback.c        |   10 +++++-----
 2 files changed, 19 insertions(+), 9 deletions(-)

--- linux-next.orig/include/linux/blk-cgroup.h	2012-03-28 13:42:26.686233288 +0800
+++ linux-next/include/linux/blk-cgroup.h	2012-03-28 14:25:16.150180560 +0800
@@ -21,6 +21,10 @@ enum blkio_policy_id {
 	BLKIO_POLICY_THROTL,		/* Throttling */
 };
 
+#define BLKIO_WEIGHT_MIN	10
+#define BLKIO_WEIGHT_MAX	1000
+#define BLKIO_WEIGHT_DEFAULT	500
+
 /* Max limits for throttle policy */
 #define THROTL_IOPS_MAX		UINT_MAX
 
@@ -209,6 +213,11 @@ extern unsigned int blkcg_get_read_iops(
 extern unsigned int blkcg_get_write_iops(struct blkio_cgroup *blkcg,
 				     dev_t dev);
 
+static inline unsigned int blkcg_weight(struct blkio_cgroup *blkcg)
+{
+	return blkcg->weight;
+}
+
 typedef void (blkio_unlink_group_fn) (void *key, struct blkio_group *blkg);
 
 typedef void (blkio_update_group_weight_fn) (void *key,
@@ -259,11 +268,12 @@ static inline void blkio_policy_unregist
 
 static inline char *blkg_path(struct blkio_group *blkg) { return NULL; }
 
-#endif
+static inline unsigned int blkcg_weight(struct blkio_cgroup *blkcg)
+{
+	return BLKIO_WEIGHT_DEFAULT;
+}
 
-#define BLKIO_WEIGHT_MIN	10
-#define BLKIO_WEIGHT_MAX	1000
-#define BLKIO_WEIGHT_DEFAULT	500
+#endif
 
 #ifdef CONFIG_DEBUG_BLK_CGROUP
 void blkiocg_update_avg_queue_size_stats(struct blkio_group *blkg);
--- linux-next.orig/mm/page-writeback.c	2012-03-28 13:42:26.678233289 +0800
+++ linux-next/mm/page-writeback.c	2012-03-28 14:26:02.694179605 +0800
@@ -905,11 +905,6 @@ static void bdi_update_dirty_ratelimit(s
 	 */
 	balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw,
 					   dirty_rate | 1);
-	/*
-	 * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw
-	 */
-	if (unlikely(balanced_dirty_ratelimit > write_bw))
-		balanced_dirty_ratelimit = write_bw;
 
 	/*
 	 * We could safely do this and return immediately:
@@ -1263,6 +1258,11 @@ static void balance_dirty_pages(struct a
 					       bdi_thresh, bdi_dirty);
 		task_ratelimit = ((u64)dirty_ratelimit * pos_ratio) >>
 							RATELIMIT_CALC_SHIFT;
+
+		if (blkcg_weight(blkcg) != BLKIO_WEIGHT_DEFAULT)
+			task_ratelimit = (u64)task_ratelimit *
+				blkcg_weight(blkcg) / BLKIO_WEIGHT_DEFAULT;
+
 		max_pause = bdi_max_pause(bdi, bdi_dirty);
 		min_pause = bdi_min_pause(bdi, max_pause,
 					  task_ratelimit, dirty_ratelimit,


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