linux-kernel - Re: [PATCH v2 1/4] mm: introduce compaction and migration for virtio ballooned pages

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Message-ID: <4FF0DEE2.5080200@kernel.org>
Date:	Mon, 02 Jul 2012 08:36:02 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Rafael Aquini <aquini@...hat.com>
CC:	linux-mm@...ck.org, Rik van Riel <riel@...hat.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2 1/4] mm: introduce compaction and migration for virtio
 ballooned pages

On 06/30/2012 10:34 AM, Rafael Aquini wrote:

>> void isolate_page_from_balloonlist(struct page* page)
>> > {
>> > 	page->mapping->a_ops->invalidatepage(page, 0);
>> > }
>> > 
>> > 	if (is_balloon_page(page) && (page_count(page) == 2)) {
>> > 		isolate_page_from_balloonlist(page);
>> > 	}
>> > 
> Humm, my feelings on your approach here: just an unecessary indirection that
> doesn't bring the desired code readability improvement.
> If the header comment statement on balloon_mapping->a_ops is not clear enough 
> on those methods usage for ballooned pages:
> 
> ..... 
> /*
>  * Balloon pages special page->mapping.
>  * users must properly allocate and initialize an instance of balloon_mapping,
>  * and set it as the page->mapping for balloon enlisted page instances.
>  *
>  * address_space_operations necessary methods for ballooned pages:
>  *   .migratepage    - used to perform balloon's page migration (as is)
>  *   .invalidatepage - used to isolate a page from balloon's page list
>  *   .freepage       - used to reinsert an isolated page to balloon's page list
>  */
> struct address_space *balloon_mapping;
> EXPORT_SYMBOL_GPL(balloon_mapping);
> .....
> 
> I can add an extra commentary, to recollect folks about that usage, next to the
> points where those callbacks are used at isolate_balloon_page() &
> putback_balloon_page(). What do you think?
> 
> 


I am not strongly against you.
It trivial nitpick must not prevent your great work. :)

Thanks!


-- 
Kind regards,
Minchan Kim
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