linux-kernel - Re: [PATCH 01/11] mm: page_alloc: handle MIGRATE_ISOLATE in free_pcppages

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Date:	Mon, 12 Dec 2011 15:23:02 +0100
From:	"Michal Nazarewicz" <mina86@...a86.com>
To:	"Marek Szyprowski" <m.szyprowski@...sung.com>,
	"Mel Gorman" <mel@....ul.ie>
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-media@...r.kernel.org, linux-mm@...ck.org,
	linaro-mm-sig@...ts.linaro.org,
	"Kyungmin Park" <kyungmin.park@...sung.com>,
	"Russell King" <linux@....linux.org.uk>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>,
	"Ankita Garg" <ankita@...ibm.com>,
	"Daniel Walker" <dwalker@...eaurora.org>,
	"Arnd Bergmann" <arnd@...db.de>,
	"Jesse Barker" <jesse.barker@...aro.org>,
	"Jonathan Corbet" <corbet@....net>,
	"Shariq Hasnain" <shariq.hasnain@...aro.org>,
	"Chunsang Jeong" <chunsang.jeong@...aro.org>,
	"Dave Hansen" <dave@...ux.vnet.ibm.com>
Subject: Re: [PATCH 01/11] mm: page_alloc: handle MIGRATE_ISOLATE in
 free_pcppages_bulk()

> On Fri, Nov 18, 2011 at 05:43:08PM +0100, Marek Szyprowski wrote:
>> From: Michal Nazarewicz <mina86@...a86.com>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 9dd443d..58d1a2e 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -628,6 +628,18 @@ static void free_pcppages_bulk(struct zone *zone, int count,
>>  			page = list_entry(list->prev, struct page, lru);
>>  			/* must delete as __free_one_page list manipulates */
>>  			list_del(&page->lru);
>> +
>> +			/*
>> +			 * When page is isolated in set_migratetype_isolate()
>> +			 * function it's page_private is not changed since the
>> +			 * function has no way of knowing if it can touch it.
>> +			 * This means that when a page is on PCP list, it's
>> +			 * page_private no longer matches the desired migrate
>> +			 * type.
>> +			 */
>> +			if (get_pageblock_migratetype(page) == MIGRATE_ISOLATE)
>> +				set_page_private(page, MIGRATE_ISOLATE);
>> +

On Mon, 12 Dec 2011 14:42:35 +0100, Mel Gorman <mel@....ul.ie> wrote:
> How much of a problem is this in practice?

IIRC, this lead to allocation being made from area marked as isolated
or some such.

> [...] I'd go as far to say that it would be preferable to drain the
> per-CPU lists after you set pageblocks MIGRATE_ISOLATE. The IPIs also have
> overhead but it will be incurred for the rare rather than the common case.

I'll look into that.

-- 
Best regards,                                         _     _
.o. | Liege of Serenely Enlightened Majesty of      o' \,=./ `o
..o | Computer Science,  Michał “mina86” Nazarewicz    (o o)
ooo +----<email/xmpp: mpn@...gle.com>--------------ooO--(_)--Ooo--
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