On Mon, May 20, 2013 at 02:02:59PM -0400, Brian Foster wrote: > On 05/19/2013 07:51 PM, Dave Chinner wrote: > > From: Dave Chinner <dchinner@xxxxxxxxxx> > > > > FSX on 512 byte block size filesystems has been failing for some > > time with corrupted data. The fault dates back to the change in > > the writeback data integrity algorithm that uses a mark-and-sweep > > approach to avoid data writeback livelocks. > > > > Unfortunately, a side effect of this mark-and-sweep approach is that > > each page will only be written once for a data integrity sync, and > > there is a condition in writeback in XFS where a page may require > > two writeback attempts to be fully written. As a result of the high > > level change, we now only get a partial page writeback during the > > integrity sync because the first pass through writeback clears the > > mark left on the page index to tell writeback that the page needs > > writeback.... > > > > The cause is writing a partial page in the clustering code. This can > > happen when a mapping boundary falls in the middle of a page - we > > end up writing back the first part of the page that the mapping > > covers, but then never revisit the page to have the remainder mapped > > and written. > > > > The fix is simple - if the mapping boundary falls inside a page, > > then simple abort clustering without touching the page. This means > > that the next ->writepage entry that write_cache_pages() will make > > is the page we aborted on, and xfs_vm_writepage() will map all > > sections of the page correctly. This behaviour is also optimal for > > non-data integrity writes, as it results in contiguous sequential > > writeback of the file rather than missing small holes and having to > > write them a "random" writes in a future pass. > > > > With this fix, all the fsx tests in xfstests now pass on a 512 byte > > block size filesystem on a 4k page machine. > > > > Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx> > > --- > > Looks good to me. > > Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx> > > > fs/xfs/xfs_aops.c | 19 +++++++++++++++++++ > > 1 file changed, 19 insertions(+) > > > > diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c > > index 2b2691b..f04eceb 100644 > > --- a/fs/xfs/xfs_aops.c > > +++ b/fs/xfs/xfs_aops.c > > @@ -725,6 +725,25 @@ xfs_convert_page( > > (xfs_off_t)(page->index + 1) << PAGE_CACHE_SHIFT, > > i_size_read(inode)); > > > > + /* > > + * If the current map does not span the entire page we are about to try > > + * to write, then give up. The only way we can write a page that spans > > + * multiple mappings in a single writeback iteration is via the > > + * xfs_vm_writepage() function. Data integrity writeback requires the > > + * entire page to be written in a single attempt, otherwise the part of > > + * the page we don't write here doesn't get written as part of the data > > + * integrity sync. > > + * > > + * For normal writeback, we also don't attempt to write partial pages > > + * here as it simply means that write_cache_pages() will see it under > > + * writeback and ignore the page until some pointin the future, at which > > + * time this will be the only page inteh file that needs writeback. > > + * Hence for more optimal IO patterns, we should always avoid partial > > + * page writeback due to multiple mappings on a page here. > > + */ Applying this with a couple of spelling fixes in this comment. Thanks for the reviews Brian. -Ben _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
