[PATCH 06/47] writeback: prevent duplicate balance_dirty_pages_ratelimited() calls

Wu Fengguang
2010-12-13T06:49:41Z

[-- Attachment #1: writeback-fix-duplicate-bdp-calls.patch --]
[-- Type: text/plain, Size: 1125 bytes --]

When dd in 512bytes, balance_dirty_pages_ratelimited() used to be called
8 times for the same page, even if 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 2010-12-08 22:43:58.000000000 +0800
+++ linux-next/mm/filemap.c 2010-12-08 22:44:23.000000000 +0800
@@ -2244,6 +2244,7 @@ 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).
@@ -2292,6 +2293,7 @@ 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);
@@ -2318,7 +2320,8 @@ again:
pos += copied;
written += copied;

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

} while (iov_iter_count(i));