Re: [PATCH v4 2/7] deactivate invalidated pages

[Minchan Kim]

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.

I want to check this.

> 
> Thanks!
> 
> 	Hannes

-- 
Kind regards,
Minchan Kim
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