On Tue, Dec 07, 2010 at 04:19:39PM +0100, Johannes Weiner wrote:
> On Wed, Dec 08, 2010 at 12:07:10AM +0900, Minchan Kim wrote:
> > On Tue, Dec 07, 2010 at 03:49:24PM +0100, Johannes Weiner wrote:
> > > On Mon, Dec 06, 2010 at 02:29:10AM +0900, Minchan Kim wrote:
> > > > Changelog since v3:
> > > > - Change function comments - suggested by Johannes
> > > > - Change function name - suggested by Johannes
> > > > - add only dirty/writeback pages to deactive pagevec
> > >
> > > Why the extra check?
> > >
> > > > @@ -359,8 +360,16 @@ unsigned long invalidate_mapping_pages(struct address_space *mapping,
> > > > if (lock_failed)
> > > > continue;
> > > >
> > > > - ret += invalidate_inode_page(page);
> > > > -
> > > > + ret = invalidate_inode_page(page);
> > > > + /*
> > > > + * If the page is dirty or under writeback, we can not
> > > > + * invalidate it now. But we assume that attempted
> > > > + * invalidation is a hint that the page is no longer
> > > > + * of interest and try to speed up its reclaim.
> > > > + */
> > > > + if (!ret && (PageDirty(page) || PageWriteback(page)))
> > > > + deactivate_page(page);
> > >
> > > The writeback completion handler does not take the page lock, so you
> > > can still miss pages that finish writeback before this test, no?
> >
> > Yes. but I think it's rare and even though it happens, it's not critical.
> > >
> > > Can you explain why you felt the need to add these checks?
> >
> > invalidate_inode_page can return 0 although the pages is !{dirty|writeback}.
> > Look invalidate_complete_page. As easiest example, if the page has buffer and
> > try_to_release_page can't release the buffer, it could return 0.
>
> Ok, but somebody still tried to truncate the page, so why shouldn't we
> try to reclaim it? The reason for deactivating at this location is
> that truncation is a strong hint for reclaim, not that it failed due
> to dirty/writeback pages.
>
> What's the problem with deactivating pages where try_to_release_page()
> failed?
If try_to_release_page fails and the such pages stay long time in pagevec,
pagevec drain often happens. I think such pages are rare so skip such pages doesn't
hurt goal of this patch.
>
> I don't think we should add more logic than necessary. If there is a
> good reason for it, it needs to get a code comment at least.
Above my comment is enough to justify it? If you agree, I can add the comment.
Thanks for careful review, Hannes.
--
Kind regards,
Minchan Kim
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