[PATCH 38/47] btrfs: wait on too many nr_async_bios

[Wu Fengguang]

Tests show that btrfs is repeatedly moving _all_ PG_dirty pages into
PG_writeback state. It's desirable to have some limit on the number of
writeback pages.

Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
---
 fs/btrfs/disk-io.c |    7 +++++++
 1 file changed, 7 insertions(+)

before patch:
	http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/tests/3G/btrfs-1dd-1M-8p-2952M-2.6.37-rc5+-2010-12-08-21-30/vmstat-dirty-300.png

after patch:
	http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/tests/3G/btrfs-1dd-1M-8p-2952M-2.6.37-rc5+-2010-12-08-21-14/vmstat-dirty-300.png

--- linux-next.orig/fs/btrfs/disk-io.c	2010-12-09 12:21:03.000000000 +0800
+++ linux-next/fs/btrfs/disk-io.c	2010-12-09 12:25:00.000000000 +0800
@@ -590,6 +590,7 @@ int btrfs_wq_submit_bio(struct btrfs_fs_
 			extent_submit_bio_hook_t *submit_bio_done)
 {
 	struct async_submit_bio *async;
+	int limit;
 
 	async = kmalloc(sizeof(*async), GFP_NOFS);
 	if (!async)
@@ -617,6 +618,12 @@ int btrfs_wq_submit_bio(struct btrfs_fs_
 
 	btrfs_queue_worker(&fs_info->workers, &async->work);
 
+	limit = btrfs_async_submit_limit(fs_info);
+
+	if (atomic_read(&fs_info->nr_async_bios) > limit)
+		wait_event(fs_info->async_submit_wait,
+			   (atomic_read(&fs_info->nr_async_bios) < limit));
+
 	while (atomic_read(&fs_info->async_submit_draining) &&
 	      atomic_read(&fs_info->nr_async_submits)) {
 		wait_event(fs_info->async_submit_wait,


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/