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Subject[patch 40/46] mm: write_cache_pages terminate quickly
2.6.28-stable review patch.  If anyone has any objections, please let us know.

------------------
From: Nick Piggin <npiggin@suse.de>

commit d5482cdf8a0aacb1e6468a97d5544f5829c8d8c4 upstream.

Terminate the write_cache_pages loop upon encountering the first page past
end, without locking the page. Pages cannot have their index change when
we have a reference on them (truncate, eg truncate_inode_pages_range
performs the same check without the page lock).

Signed-off-by: Nick Piggin <npiggin@suse.de>
Cc: Chris Mason <chris.mason@oracle.com>
Cc: Dave Chinner <david@fromorbit.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
mm/page-writeback.c | 32 ++++++++++++++++----------------
1 file changed, 16 insertions(+), 16 deletions(-)
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -911,15 +911,24 @@ retry:
for (i = 0; i < nr_pages; i++) {
struct page *page = pvec.pages[i];

- done_index = page->index + 1;
-
/*
- * At this point we hold neither mapping->tree_lock nor
- * lock on the page itself: the page may be truncated or
- * invalidated (changing page->mapping to NULL), or even
- * swizzled back from swapper_space to tmpfs file
- * mapping
+ * At this point, the page may be truncated or
+ * invalidated (changing page->mapping to NULL), or
+ * even swizzled back from swapper_space to tmpfs file
+ * mapping. However, page->index will not change
+ * because we have a reference on the page.
*/
+ if (page->index > end) {
+ /*
+ * can't be range_cyclic (1st pass) because
+ * end == -1 in that case.
+ */
+ done = 1;
+ break;
+ }
+
+ done_index = page->index + 1;
+
lock_page(page);

/*
@@ -936,15 +945,6 @@ continue_unlock:
continue;
}

- if (page->index > end) {
- /*
- * can't be range_cyclic (1st pass) because
- * end == -1 in that case.
- */
- done = 1;
- goto continue_unlock;
- }
-
if (!PageDirty(page)) {
/* someone wrote it for us */
goto continue_unlock;


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