linux-kernel - Re: [PATCH v3 8/9] memory-hotplug: fix NR_FREE

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Date:	Fri, 19 Oct 2012 03:41:47 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	wency@...fujitsu.com
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	rientjes@...gle.com, liuj97@...il.com, len.brown@...el.com,
	benh@...nel.crashing.org, paulus@...ba.org, minchan.kim@...il.com,
	akpm@...ux-foundation.org, isimatu.yasuaki@...fujitsu.com,
	Christoph Lameter <cl@...ux.com>
Subject: Re: [PATCH v3 8/9] memory-hotplug: fix NR_FREE_PAGES mismatch

On Fri, Oct 19, 2012 at 2:46 AM,  <wency@...fujitsu.com> wrote:
> From: Wen Congyang <wency@...fujitsu.com>
>
> NR_FREE_PAGES will be wrong after offlining pages. We add/dec NR_FREE_PAGES
> like this now:
> 1. mova all pages in buddy system to MIGRATE_ISOLATE, and dec NR_FREE_PAGES

move?

> 2. don't add NR_FREE_PAGES when it is freed and the migratetype is MIGRATE_ISOLATE
> 3. dec NR_FREE_PAGES when offlining isolated pages.
> 4. add NR_FREE_PAGES when undoing isolate pages.
>
> When we come to step 3, all pages are in MIGRATE_ISOLATE list, and NR_FREE_PAGES
> are right. When we come to step4, all pages are not in buddy system, so we don't
> change NR_FREE_PAGES in this step, but we change NR_FREE_PAGES in step3. So
> NR_FREE_PAGES is wrong after offlining pages. So there is no need to change
> NR_FREE_PAGES in step3.

Sorry, I don't understand this two paragraph. Can  you please elaborate more?

and one more trivial question: why do we need to call
undo_isolate_page_range() from
__offline_pages()?


>
> This patch also fixs a problem in step2: if the migratetype is MIGRATE_ISOLATE,
> we should not add NR_FRR_PAGES when we remove pages from pcppages.

Why drain_all_pages doesn't work?
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