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Subject[PATCH 2/4] writeback: avoid duplicate balance_dirty_pages_ratelimited() calls
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 2011-04-13 16:46:01.000000000 +0800
+++ linux-next/mm/filemap.c 2011-04-13 16:47:26.000000000 +0800
@@ -2313,6 +2313,7 @@ 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).
@@ -2361,6 +2362,7 @@ 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);
@@ -2387,7 +2389,8 @@ again:
pos += copied;
written += copied;

- balance_dirty_pages_ratelimited(mapping);
+ if (!dirty)
+ balance_dirty_pages_ratelimited(mapping);

} while (iov_iter_count(i));




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