linux-kernel - Re: [PATCH v2 7/7] mm/migrate: remove result argument on page allocation function for migration

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Date:	Mon, 9 Dec 2013 16:40:06 +0000
From:	Christoph Lameter <cl@...ux.com>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Rafael Aquini <aquini@...hat.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Joonsoo Kim <js1304@...il.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Vlastimil Babka <vbabka@...e.cz>,
	Zhang Yanfei <zhangyanfei@...fujitsu.com>
Subject: Re: [PATCH v2 7/7] mm/migrate: remove result argument on page
 allocation function for migration

On Mon, 9 Dec 2013, Joonsoo Kim wrote:

> First, we don't use error number in fail case. Call-path related to
> new_page_node() is shown in the following.
>
> do_move_page_to_node_array() -> migrate_pages() -> unmap_and_move()
> -> new_page_node()
>
> If unmap_and_move() failed, migrate_pages() also returns err, and then
> do_move_page_to_node_array() skips to set page's status to user buffer.
> So we don't need to set error number to each pages on failure case.

I dont get this. new_page_node() sets the error condition in the
page_to_node array before this patch. There is no post processing in
do_move_page_to_node_array(). The function simply returns and relies on
new_page_node() to have set the page status. do_move_pages() then returns
the page status back to userspace. How does the change preserve these
diagnostics?

> Next, we don't need to set node id of the new page in unmap_and_move(),
> since it cannot be different with pm->node. In new_page_node(), we always
> try to allocate the page in exact node by referencing pm->node. So it is
> sufficient to set node id of the new page in new_page_node(), instead of
> unmap_and_move().

Thats a good thought.


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