linux-kernel - Re: Accounting problem of MIGRATE

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Message-ID: <4FE7BCAD.4090002@kernel.org>
Date:	Mon, 25 Jun 2012 10:19:41 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
CC:	undisclosed-recipients:;
	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Aaditya Kumar <aaditya.kumar.30@...il.com>,
	Mel Gorman <mel@....ul.ie>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Accounting problem of MIGRATE_ISOLATED freed page

On 06/23/2012 11:59 AM, KOSAKI Motohiro wrote:

> 
> One more.
> 
> 
>> +/*
>> + * NOTE:
>> + * Don't use set_pageblock_migratetype(page, MIGRATE_ISOLATE) direclty.
>> + * Instead, use {un}set_pageblock_isolate.
>> + */
>>  void set_pageblock_migratetype(struct page *page, int migratetype)
>>  {
>>         if (unlikely(page_group_by_mobility_disabled))
> 
> I don't think we need this comment. please just add BUG_ON.

It adds new condition check in __rmqueue_fallback.
If it's okay, no problem.

But as you know, calling MIGRATE_ISOLATE is very very rare and we can
make sure it's no problem on existing code. So the problem is future
user and I hope they can look at the code comment before using and we mm
have strong review system rather than other subsystem, I believe. :)

If you can't agree, I am willing to add BUG_ON but not sure others
like it. (Especially, Mel).

-- 
Kind regards,
Minchan Kim
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