On Tue, Aug 20, 2013 at 2:48 PM, Dave Chinner <da...@fromorbit.com> wrote: > On Tue, Aug 20, 2013 at 09:42:34AM -0700, Andy Lutomirski wrote: >> On Tue, Aug 20, 2013 at 9:00 AM, Jan Kara <j...@suse.cz> wrote: >> > On Mon 19-08-13 21:14:44, Andy Lutomirski wrote: >> >> >> I could require ->writepages *and* ->flush_cmtime to handle the time >> >> >> update, but that would complicate non-transactional filesystems. >> >> >> Those filesystems should just flush cmtime at the end of writepages. >> >> > >> >> > do_writepages() is the wrong place to do such updates - we can get >> >> > writeback directly through .writepage, so the time updates need to >> >> > be in .writepage. That first .writepage call will clear the bit on >> >> > the mapping, so it's only done on the first call to .writepage on >> >> > the given mapping. >> >> >> >> Last time I checked, all the paths that actually needed the timestamp >> >> update went through .writepages. I'll double-check. >> > kswapd can call just .writepage to do the writeout so timestamp update >> > should be handled there as well. Otherwise all pages in a mapping can be >> > cleaned without timestamp being updated. >> >> OK, I'll fix that. >> >> > >> > Which btw made me realize that even your scheme doesn't completely make >> > sure timestamp is updated after mmap write - if you have pages 0 and 1, you >> > write to both of them - CMTIME flag gets set. Then fsync_range(fd, 0, 4096) >> > is called. We write the page 0, writeprotect it, update timestamps. But >> > page 1 is still writeable so writes to it won't set CMTIME flag, neither >> > update the timestamp... Not that I think this can be reasonably solved but >> > it is a food for thought. >> >> This should already work. AS_CMTIME is set when the pte goes from >> dirty to clean, not when the pte goes from wp to writable. So >> whenever clear_page_dirty_for_io is called on page 1, AS_CMTIME will >> be set and a subsequent writepages call will update the timestamp. > > Oh, I missed that - I thought you were setting AS_CMTIME during > .page_mkwrite. > > Setting it in clear_page_dirty_for_io() is too late for filesystems > to include it in their existing transactions during .writepage, (at > least for XFs and ext4) because they do their delayed allocation > transactions before changing page state....
Couldn't it go between mpage_map_and_submit_extent and ext4_journal_stop in ext4_writepages? > > Cheers, > > Dave. > -- > Dave Chinner > da...@fromorbit.com -- Andy Lutomirski AMA Capital Management, LLC -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
