path: root/mm
diff options
authorDave Chinner <dchinner@redhat.com>2010-06-09 10:37:20 +1000
committerLinus Torvalds <torvalds@linux-foundation.org>2010-06-08 18:12:44 -0700
commitd87815cb2090e07b0b0b2d73dc9740706e92c80c (patch)
tree0e23b40fce5b09c94dab2bf773601b310d8d9b09 /mm
parent254c8c2dbf0e06a560a5814eb90cb628adb2de66 (diff)
writeback: limit write_cache_pages integrity scanning to current EOF
sync can currently take a really long time if a concurrent writer is extending a file. The problem is that the dirty pages on the address space grow in the same direction as write_cache_pages scans, so if the writer keeps ahead of writeback, the writeback will not terminate until the writer stops adding dirty pages. For a data integrity sync, we only need to write the pages dirty at the time we start the writeback, so we can stop scanning once we get to the page that was at the end of the file at the time the scan started. This will prevent operations like copying a large file preventing sync from completing as it will not write back pages that were dirtied after the sync was started. This does not impact the existing integrity guarantees, as any dirty page (old or new) within the EOF range at the start of the scan will still be captured. This patch will not prevent sync from blocking on large writes into holes. That requires more complex intervention while this patch only addresses the common append-case of this sync holdoff. Signed-off-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
1 files changed, 15 insertions, 0 deletions
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index b3dbb8040ed..bbd396ac954 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -851,7 +851,22 @@ int write_cache_pages(struct address_space *mapping,
if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
range_whole = 1;
cycled = 1; /* ignore range_cyclic tests */
+ /*
+ * If this is a data integrity sync, cap the writeback to the
+ * current end of file. Any extension to the file that occurs
+ * after this is a new write and we don't need to write those
+ * pages out to fulfil our data integrity requirements. If we
+ * try to write them out, we can get stuck in this scan until
+ * the concurrent writer stops adding dirty pages and extending
+ * EOF.
+ */
+ if (wbc->sync_mode == WB_SYNC_ALL &&
+ wbc->range_end == LLONG_MAX) {
+ end = i_size_read(mapping->host) >> PAGE_CACHE_SHIFT;
+ }
done_index = index;
while (!done && (index <= end)) {