On Tue, Aug 05, 2008 at 11:24:39PM +0530, Aneesh Kumar K.V wrote: > Hi, > > I am trying to understand the expectation on filesystem > writepages by __fsync_super -> generic_sync_sb_inodes call path. > __fsync_super make two calls to generic_sync_sb_inodes and the > second call is made with WB_SYNC_ALL. The problem is, i am finding > multiple ways we may 'break' from the generic_sync_sb_inodes > while (!list_empty(&sb->s_io)) loop. For ex: > > a) When wbc->nr_to_write <=0 > This should normally indicate that we wrote more than we requested > That means we have more dirty pages . So why break from loop ? > This may be ok for nr_to_write limited writeback. But is it ok > for __fsync_super ? > > b) pages_skipped != wbc->pages_skipped. > That means writepages was not able to write some of the pages > and it redirtied the same. We add such inode to s_dirty list. But > we don't loop through the s_dirty list later trying to write the > dirty pages. We actually call generic_sync_sb_inodes again. That > can actually cause s_dirty list content to move to s_io once > via queue_io. But then we can have pages skipped again in the second > call to generic_sync_sb_inodes ? > > > Shouldn't we have a variant that actually loop trough s_dirty and s_more_io > list MULTIPLE times and make sure we force all the dirty pages to disk > before __fsync_super returns ? Or is there an expectation from file > system writepages that would make sure calling generic_sync_sb_inodes > TWICE would guarantee that ? > > The problem I am looking at is listed here. http://thread.gmane.org/gmane.comp.file-systems.ext4/8277 basically a mount -o remount,ro followed by a sync is indicating that there are dirty pages left after remount,ro -aneesh -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
