[PATCH] btrfs: lower the dirty balance poll interval

[Wu Fengguang]

Tests show that the original large intervals can easily make the dirty
limit exceeded on 100 concurrent dd's. So adapt to as large as the
next check point selected by the dirty throttling algorithm.

Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
---
 fs/btrfs/file.c |    2 ++
 1 file changed, 2 insertions(+)

--- linux-next.orig/fs/btrfs/file.c	2011-11-17 20:18:51.000000000 +0800
+++ linux-next/fs/btrfs/file.c	2011-11-17 20:18:55.000000000 +0800
@@ -1168,6 +1168,8 @@ static noinline ssize_t __btrfs_buffered
 	nrptrs = min((iov_iter_count(i) + PAGE_CACHE_SIZE - 1) /
 		     PAGE_CACHE_SIZE, PAGE_CACHE_SIZE /
 		     (sizeof(struct page *)));
+	nrptrs = min(nrptrs, current->nr_dirtied_pause - current->nr_dirtied);
+	nrptrs = max(nrptrs, 8);
 	pages = kmalloc(nrptrs * sizeof(struct page *), GFP_KERNEL);
 	if (!pages)
 		return -ENOMEM;
--
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