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. --Andy -- 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/
