On Fri 02-08-13 11:26:24, Dave Jones wrote: > On Fri, Aug 02, 2013 at 04:23:24PM +0200, Jan Kara wrote: > > On Thu 01-08-13 00:42:12, Jan Kara wrote: > > > Inode size can arbitrarily change while writeback is in progress. This > > > can have various strange effects when we use one value of i_size for one > > > decision during writeback and another value of i_size for a different > > > decision during writeback. In particular a check for lblk < blocks in > > > mpage_map_and_submit_buffers() causes problems when i_size is reduced > > > while writeback is running because we can end up not using all blocks > > > we've allocated. Thus these blocks are leaked and also delalloc > > > accounting gets wrong manifesting as a warning like: > > > > > > ext4_da_release_space:1333: ext4_da_release_space: ino 12, to_free 1 > > > with only 0 reserved data blocks > > > > > > The problem can happen only when blocksize < pagesize because the check > > > for size is performed only after the first iteration of the mapping > > > loop. > > > > > > Fix the problem by removing the size check from the mapping loop. We > > > have an extent allocated so we have to use it all before checking for > > > i_size. We may call add_page_bufs_to_extent() unnecessarily but that > > > function won't do anything if passed block number is beyond file size. > > > > > > Also to avoid future surprises like this sample inode size when > > > starting writeback in ext4_writepages() and then use this sampled size > > > throughout the writeback call stack. > > Ted, please disregard this patch. It is buggy. I'll send a better fix > > soon. > > I was about to post that I was seeing fsx failures on 1k filesystems > on a kernel with this patch. > > Is that the same thing you're seeing ? Likely, I saw fsstress failures with it. But fsx would likely fail as well - the writing of tail page was hosed. Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
