Re: [PATCH] jfs: clear PAGECACHE_TAG_DIRTY for no-write pages

Fengguang Wu
2007-12-28T11:42:50Z

On Fri, Dec 28, 2007 at 12:33:46PM +0100, Peter Zijlstra wrote:
>
> On Fri, 2007-12-28 at 16:03 +0800, Fengguang Wu wrote:
> > Andrew,
> >
> > This patch fixed the 'pdflush stuck in D state' bug
> > http://bugzilla.kernel.org/show_bug.cgi?id=9291
> > and should be pushed to mainline ASAP.
> > ---
> >
> > When JFS decides to drop a dirty metapage, it simply clears the META_dirty bit
> > and leave alone the PG_dirty and PAGECACHE_TAG_DIRTY bits.
> >
> > When such no-write page goes to metapage_writepage(), the `relic'
> > PAGECACHE_TAG_DIRTY tag should be cleared, to prevent pdflush from
> > repeatedly trying to sync them.
> >
> > Also, avoid the redirty when a bio submission is planned.
> >
> > Tested-by: Markus Rehbach <Markus.Rehbach@gmx.de>
> > Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
> > ---
>
> > +++ b/fs/jfs/jfs_metapage.c
>
> > @@ -449,9 +450,15 @@ static int metapage_writepage(struct page *page, struct writeback_control *wbc)
> > goto dump_bio;
> >
> > submit_bio(WRITE, bio);
> > - }
> > - if (redirty)
> > + } else if (redirty) {
> > redirty_page_for_writepage(wbc, page);
> > + } else {
> > + write_lock_irq(&mapping->tree_lock);
> > + radix_tree_tag_clear(&mapping->page_tree,
> > + page_index(page),
> > + PAGECACHE_TAG_DIRTY);
> > + write_unlock_irq(&mapping->tree_lock);
> > + }
>
> I'm not liking this open-coded tag_clear, although I currently fail to
> come up with a nice solution.

Another option is to release/drop such pages ASAP. But what if the
metapage_writepage() is called even before we have the chance to
release it?