On Mon 02-06-08 15:29:56, Aneesh Kumar K.V wrote:
> On Mon, Jun 02, 2008 at 11:35:00AM +0200, Jan Kara wrote:
> > > BUG_ON(buffer_locked(bh));
> > > if (buffer_dirty(bh))
> > > mpage_add_bh_to_extent(mpd, logical, bh);
> > > diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> > > index 789b6ad..655b8bf 100644
> > > --- a/mm/page-writeback.c
> > > +++ b/mm/page-writeback.c
> > > @@ -881,7 +881,12 @@ int write_cache_pages(struct address_space *mapping,
> > > pagevec_init(&pvec, 0);
> > > if (wbc->range_cyclic) {
> > > index = mapping->writeback_index; /* Start from prev offset */
> > > - end = -1;
> > > + /*
> > > + * write only till the specified range_end even in cyclic mode
> > > + */
> > > + end = wbc->range_end >> PAGE_CACHE_SHIFT;
> > > + if (!end)
> > > + end = -1;
> > > } else {
> > > index = wbc->range_start >> PAGE_CACHE_SHIFT;
> > > end = wbc->range_end >> PAGE_CACHE_SHIFT;
> > Are you sure you won't break other users of range_cyclic with this
> > change?
> >
> I haven't run any specific test to verify that. The concern was that if
> we force cyclic mode for writeout in delalloc we may be starting the
> writeout from a different offset than specified and would be writing
> more. So the changes was to use the offset specified. A quick look at
> the kernel suggested most of them had range_end as 0 with cyclic_mode.
> I haven't audited the full kernel. I will do that. Meanwhile if you
> think it is risky to make this changes i guess we should drop this
> part. But i guess we can keep the below change
Hmm, I've just got an idea that it may be better to introduce a new flag
for wbc like range_cont and it would mean that we start scan at
writeback_index (we use range_start if writeback_index is not set) and
end with range_end. That way we don't have to be afraid of interference
with other range_cyclic users and in principle, range_cyclic is originally
meant for other uses...
> + index = mapping->writeback_index;
> + if (!range_cyclic) {
> + /*
> + * We force cyclic write out of pages. If the
> + * caller didn't request for range_cyclic update
> + * set the writeback_index to what the caller requested.
> + */
> + mapping->writeback_index = wbc->range_start >> PAGE_CACHE_SHIFT;
> + }
Honza
--
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
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