From mboxrd@z Thu Jan  1 00:00:00 1970
Subject: RE: Which is the proper way to bring in the backing store behind
	an inode as an struct page?
From: Ram Pai <linuxram@us.ibm.com>
In-Reply-To: <F989B1573A3A644BAB3920FBECA4D25A6EBEEE@orsmsx407>
References: <F989B1573A3A644BAB3920FBECA4D25A6EBEEE@orsmsx407>
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Date: 02 Jul 2004 22:52:04 -0700
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To: "Perez-Gonzalez, Inaky" <inaky.perez-gonzalez@intel.com>
Cc: "Chen, Kenneth W" <kenneth.w.chen@intel.com>, linux-mm@kvack.org
List-ID: <linux-mm.kvack.org>

On Fri, 2004-07-02 at 17:37, Perez-Gonzalez, Inaky wrote:
> Hi Ken
> 
> > From: Chen, Kenneth W [mailto:kenneth.w.chen@intel.com]
> > 
> > Perez-Gonzalez, Inaky wrote on Thursday, July 01, 2004 11:35 PM
> > > Dummy question that has been evading me for the last hours. Can you
> > > help? Please bear with me here, I am a little lost in how to deal
> > > with inodes and the cache.
> > >
> > > ....
> > >
> > > Thus, what I need is a way that given the pair (inode,pgoff)
> > > returns to me the 'struct page *' if the thing is cached in memory or
> > > pulls it up from swap/file into memory and gets me a 'struct page *'.
> > >
> > > Is there a way to do this?
> > 
> > find_get_page() might be the one you are looking for.
> 
> Something like this? [I am trying blindly]

> page = find_get_page (inode->i_mapping, pgoff)

I would like at the logic of do_generic_mapping_read(). The code below
is perhaps roughly what you want.

page = find_get_page(inode->i_mapping, pgoff);
if(unlikely(page==NULL)) {

	page = page_cache_alloc_cold(mapping);
	if (!page) {
                /* NO LUCK SORRY :-( */
        }

        if(add_to_page_cache_lru(page, mapping, pgoff, GFP_KERNEL)) {
                /* NO LUCK SORRY :-( */
        }
}
if (!PageUptodate(page)) { 
     lock_page(page);
     mapping->a_ops->readpage(filp /*i guess this can be null */,
			 page);
}
	
	


	

> 
> Under which circumstances will this fail? [I am guessing the only ones
> are if the page offset is out of the limits of the map]. What about 
> i_mapping? When is it not defined? [ie: NULL].
> 
> Thanks
> 
> IA+-aky PA(C)rez-GonzA!lez -- Not speaking for Intel -- all opinions are my own (and my fault)
> --
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