From: Miklos Szeredi <mszeredi@suse.cz>

The function do_lo_send_aops() should call
balance_dirty_pages_ratelimited() after each page similarly to
generic_file_buffered_write().

Without this, writing the loop device directly (not through a
filesystem) is very slow, and also slows the whole system down,
because nr_dirty is constantly over the limit.

Beware: this patch without the fix to balance_dirty_pages() makes a
loopback mounted filesystem prone to deadlock.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---

Index: linux/drivers/block/loop.c
===================================================================
--- linux.orig/drivers/block/loop.c	2007-02-27 14:40:55.000000000 +0100
+++ linux/drivers/block/loop.c	2007-02-27 14:41:08.000000000 +0100
@@ -275,6 +275,8 @@ static int do_lo_send_aops(struct loop_d
 		pos += size;
 		unlock_page(page);
 		page_cache_release(page);
+		balance_dirty_pages_ratelimited(mapping);
+		cond_resched();
 	}
 	ret = 0;
 out:

--
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