linux-kernel - Re: [PATCH] mm: use a radix-tree to make do_move

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Date:	Mon, 13 Oct 2008 09:09:30 -0700
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Brice Goglin <Brice.Goglin@...ia.fr>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	nathalie.furmento@...ri.fr
Subject: Re: [PATCH] mm: use a radix-tree to make do_move_pages() complexity
 linear

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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