Re: [PATCH v3 8/9] memory-hotplug: fix NR_FREE_PAGES mismatch

[KOSAKI Motohiro]

On Fri, Oct 19, 2012 at 2:46 AM,  <wency@xxxxxxxxxxxxxx> wrote:
> From: Wen Congyang <wency@xxxxxxxxxxxxxx>
>
> 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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