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Message-Id: <20110303074948.914547023@intel.com>
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Date: Thu, 03 Mar 2011 14:45:07 +0800
From: Wu Fengguang <fengguang.wu@intel.com>
To: Andrew Morton <akpm@linux-foundation.org>
CC: Jan Kara <jack@suse.cz>, Wu Fengguang <fengguang.wu@intel.com>
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Subject: [PATCH 02/27] writeback: avoid duplicate balance_dirty_pages_ratelimited() calls
References: <20110303064505.718671603@intel.com>
Content-Disposition: inline; filename=writeback-fix-duplicate-bdp-calls.patch
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When dd in 512bytes, balance_dirty_pages_ratelimited() could be called 8
times for the same page, but obviously the page is only dirtied once.

Fix it with a (slightly racy) PageDirty() test.

Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
---
 mm/filemap.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- linux-next.orig/mm/filemap.c	2011-03-02 14:18:52.000000000 +0800
+++ linux-next/mm/filemap.c	2011-03-02 14:20:07.000000000 +0800
@@ -2253,6 +2253,7 @@ static ssize_t generic_perform_write(str
 	long status = 0;
 	ssize_t written = 0;
 	unsigned int flags = 0;
+	unsigned int dirty;
 
 	/*
 	 * Copies from kernel address space cannot fail (NFSD is a big user).
@@ -2301,6 +2302,7 @@ again:
 		pagefault_enable();
 		flush_dcache_page(page);
 
+		dirty = PageDirty(page);
 		mark_page_accessed(page);
 		status = a_ops->write_end(file, mapping, pos, bytes, copied,
 						page, fsdata);
@@ -2327,7 +2329,8 @@ again:
 		pos += copied;
 		written += copied;
 
-		balance_dirty_pages_ratelimited(mapping);
+		if (!dirty)
+			balance_dirty_pages_ratelimited(mapping);
 
 	} while (iov_iter_count(i));