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Subject[patch 32/40] mm: write_cache_pages cleanups
2.6.27-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Nick Piggin <npiggin@suse.de>

commit 5a3d5c9813db56a75934eb1015367fda23a8b0b4 upstream.

Get rid of some complex expressions from flow control statements, add a
comment, remove some duplicate code.

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 | 34 ++++++++++++++++++++++------------
1 file changed, 22 insertions(+), 12 deletions(-)

--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -902,11 +902,14 @@ int write_cache_pages(struct address_spa
}
retry:
done_index = index;
- while (!done && (index <= end) &&
- (nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
- PAGECACHE_TAG_DIRTY,
- min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1))) {
- unsigned i;
+ while (!done && (index <= end)) {
+ int i;
+
+ nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
+ PAGECACHE_TAG_DIRTY,
+ min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
+ if (nr_pages == 0)
+ break;

for (i = 0; i < nr_pages; i++) {
struct page *page = pvec.pages[i];
@@ -922,7 +925,16 @@ retry:
*/
lock_page(page);

+ /*
+ * Page truncated or invalidated. We can freely skip it
+ * then, even for data integrity operations: the page
+ * has disappeared concurrently, so there could be no
+ * real expectation of this data interity operation
+ * even if there is now a new, dirty page at the same
+ * pagecache address.
+ */
if (unlikely(page->mapping != mapping)) {
+continue_unlock:
unlock_page(page);
continue;
}
@@ -933,18 +945,15 @@ retry:
* end == -1 in that case.
*/
done = 1;
- unlock_page(page);
- continue;
+ goto continue_unlock;
}

if (wbc->sync_mode != WB_SYNC_NONE)
wait_on_page_writeback(page);

if (PageWriteback(page) ||
- !clear_page_dirty_for_io(page)) {
- unlock_page(page);
- continue;
- }
+ !clear_page_dirty_for_io(page))
+ goto continue_unlock;

ret = (*writepage)(page, wbc, data);

@@ -968,7 +977,8 @@ retry:
}

if (wbc->sync_mode == WB_SYNC_NONE) {
- if (--wbc->nr_to_write <= 0)
+ wbc->nr_to_write--;
+ if (wbc->nr_to_write <= 0)
done = 1;
}
if (wbc->nonblocking && bdi_write_congested(bdi)) {


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