linux-kernel - Re: [patch 03/19] define page_file

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Date:	Tue, 8 Jan 2008 17:28:56 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Christoph Lameter <clameter@....com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Lee Schermerhorn <lee.schermerhorn@...com>
Subject: Re: [patch 03/19] define page_file_cache() function

On Tue, 8 Jan 2008 14:18:40 -0800 (PST)
Christoph Lameter <clameter@....com> wrote:

> On Tue, 8 Jan 2008, Rik van Riel wrote:
> 
> > Define page_file_cache() function to answer the question:
> > 	is page backed by a file?
> 
> > +static inline int page_file_cache(struct page *page)
> > +{
> > +	if (PageSwapBacked(page))
> > +		return 0;
> 
> Could we call this PageNotFileBacked or so? PageSwapBacked is true for 
> pages that are RAM based. Its a bit confusing.

PageNotFileBacked confuses me a little, since shared memory segments live
in tmpfs and are kinda sorta file backed, but go to swap instead of to a
filesystem when there is memory pressure.

I'm always open to better naming ideas, though.

> > Index: linux-2.6.24-rc6-mm1/mm/migrate.c
> > ===================================================================
> > --- linux-2.6.24-rc6-mm1.orig/mm/migrate.c	2008-01-02 12:37:14.000000000 -0500
> > +++ linux-2.6.24-rc6-mm1/mm/migrate.c	2008-01-02 12:37:22.000000000 -0500
> > @@ -546,6 +546,8 @@ static int move_to_new_page(struct page 
> >  	/* Prepare mapping for the new page.*/
> >  	newpage->index = page->index;
> >  	newpage->mapping = page->mapping;
> > +	if (PageSwapBacked(page))
> > +		SetPageSwapBacked(newpage);
> >  
> >  	mapping = page_mapping(page);
> >  	if (!mapping)
> 
> That hunk belongs into migrate_page_copy()? Or is there a reason that we 
> need this flag that early?

We want the page added to the right LRU list.  I'll have to re-read the
migration code to make sure whether the above can or cannot be done in
migrate_page_copy() - I agree it would fit in better there.

Thanks for the suggestions.

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