linux-kernel - Re: [05/17] vunmap: return page array

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Message-Id: <20070920094720.46e781ec.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Thu, 20 Sep 2007 09:47:20 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Christoph Lameter <clameter@....com>
Cc:	Christoph Hellwig <hch@....de>, Mel Gorman <mel@...net.ie>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	David Chinner <dgc@....com>, Jens Axboe <jens.axboe@...cle.com>
Subject: Re: [05/17] vunmap: return page array

On Wed, 19 Sep 2007 15:15:58 -0700 (PDT)
Christoph Lameter <clameter@....com> wrote:

> On Wed, 19 Sep 2007, KAMEZAWA Hiroyuki wrote:
> 
> > Hmm, I don't like returning array which someone allocated in past and forgot.
> 
> But that is exactly the point. There is no need to keep track of the 
> information that is of no interest until the disposition of the mapping.
> 
yes. But I think neat style of this kind function is
==
/* If array != NULL, pointer of unmapped pages are stored in array[] */
extern int vunmap(const void *addr, struct page **array);
==
But yes, this costs.

> > And, area->page[] array under vmalloc() is allocated as following (in -rc6-mm1)
> > ==
> >        if (array_size > PAGE_SIZE) {
> >                 pages = __vmalloc_node(array_size, gfp_mask | __GFP_ZERO,
> >                                         PAGE_KERNEL, node);
> >                 area->flags |= VM_VPAGES;
> >         } else {
> >                 pages = kmalloc_node(array_size,
> >                                 (gfp_mask & GFP_RECLAIM_MASK) | __GFP_ZERO,
> >                                 node);
> >         }
> > ==
> > A bit complicating.
> 
> Not at all. You can pass a __vmalloc'ed entity to vmap if you add VM_VPAGES 
> to the flags passed to it.
> 
> > At least, please add comments "How to free page-array returned by vummap"
> 
> But that depends on how the vmap was called. The caller knows what he has 
> done to acquire the memory and therefore also knows how to get rid of it.
>  
Hm, it seems all your patch are for hiding usage of vmalloc()/vmap().
If freeing pages[] array is also hidden in your patch's context, no problem.

Thanks,
-Kame


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