linux-kernel - Re: Accounting problem of MIGRATE

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Date:	Wed, 20 Jun 2012 21:39:07 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Aaditya Kumar <aaditya.kumar.30@...il.com>,
	Mel Gorman <mel@....ul.ie>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Accounting problem of MIGRATE_ISOLATED freed page

>> number of isolate page block is almost always 0. then if we have such counter,
>> we almost always can avoid zone->lock. Just idea.
>
> Yeb. I thought about it but unfortunately we can't have a counter for MIGRATE_ISOLATE.
> Because we have to tweak in page free path for pages which are going to free later after we
> mark pageblock type to MIGRATE_ISOLATE.

I mean,

if (nr_isolate_pageblock != 0)
   free_pages -= nr_isolated_free_pages(); // your counting logic

return __zone_watermark_ok(z, alloc_order, mark,
                              classzone_idx, alloc_flags, free_pages);


I don't think this logic affect your race. zone_watermark_ok() is already
racy. then new little race is no big matter.
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