Message-ID: <48F372BA.7020505@linux-foundation.org>
Date: Mon, 13 Oct 2008 09:09:30 -0700
From: Christoph Lameter <cl@linux-foundation.org>
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To: Brice Goglin <Brice.Goglin@inria.fr>
CC: Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org,
       linux-mm@kvack.org, nathalie.furmento@labri.fr
Subject: Re: [PATCH] mm: use a radix-tree to make do_move_pages() complexity
 linear
References: <48EDF9DA.7000508@inria.fr> <20081010125010.164bcbb8.akpm@linux-foundation.org> <48EFB6E6.4080708@inria.fr> <48EFBBE9.5000703@linux-foundation.org> <48F069B8.6050709@inria.fr>
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Brice Goglin wrote:
> * One thing that bothers me is move_pages() returning -ENOENT when no
> page are given to migrate_pages(). I don't see why having 100/100 pages
> not migrated would return a different error than having only 99/100
> pages not migrated. We have the status array to place -ENOENT for all
> these pages. If the user doesn't know where his pages are allocated, he
> shouldn't get a different return value depending on how many pages were
> already on the right node. And actually, this convention makes
> user-space application harder to write since you need to treat -ENOENT
> as a success unless you already knew for sure where your pages were
> allocated. And the big thing is that this convention makes the chunking
> painfully/uselessly more complex. Breaking user-ABI is bad, but fixing
> crazy ABI...
>   
I do not think that move_pages() is used that frequently. Changing the 
API slightly as you suggest would not be that big of a deal.

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