mm: write_cache_pages terminate quickly
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>
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 2e8c2b0..0d986c1 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -911,15 +911,24 @@
for (i = 0; i < nr_pages; i++) {
struct page *page = pvec.pages[i];
+ /*
+ * 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;
- /*
- * 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
- */
lock_page(page);
/*
@@ -936,15 +945,6 @@
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;
