linux-kernel - Re: [PATCH 1/11] Add __GFP_MOVABLE flag and update callers

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Message-ID: <Pine.LNX.4.64.0611231457070.23409@skynet.skynet.ie>
Date:	Thu, 23 Nov 2006 15:00:16 +0000 (GMT)
From:	Mel Gorman <mel@....ul.ie>
To:	Christoph Lameter <clameter@....com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/11] Add __GFP_MOVABLE flag and update callers

On Tue, 21 Nov 2006, Christoph Lameter wrote:

> On Tue, 21 Nov 2006, Mel Gorman wrote:
>
>> On Tue, 21 Nov 2006, Christoph Lameter wrote:
>>
>>> Are GFP_HIGHUSER allocations always movable? It would reduce the size of
>>> the patch if this would be added to GFP_HIGHUSER.
>> No, they aren't. Page tables allocated with HIGHPTE are currently not movable
>> for example. A number of drivers (infiniband for example) also use
>> __GFP_HIGHMEM that are not movable.
>
> HIGHPTE with __GFP_USER set? This is a page table page right?
> pte_alloc_one does currently not set GFP_USER:
>

What is __GFP_USER? The difference between GFP_USER and GFP_KERNEL is only 
in the use of __GFP_HARDWALL. But HARDWALL on it's own is not enough to 
distinguish movable and non-movable.

> struct page *pte_alloc_one(struct mm_struct *mm, unsigned long address)
> {
>        struct page *pte;
>
> #ifdef CONFIG_HIGHPTE
>        pte =
> alloc_pages(GFP_KERNEL|__GFP_HIGHMEM|__GFP_REPEAT|__GFP_ZERO, 0);
> #else
>        pte = alloc_pages(GFP_KERNEL|__GFP_REPEAT|__GFP_ZERO, 0);
> #endif
>        return pte;
> }
>
> How does infiniband insure that page migration does not move those pages?
>

I have not looked closely at infiniband and how it uses it's pages.

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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