On Fri, Oct 19, 2012 at 2:46 AM,  [off-list ref] wrote:

From: Wen Congyang <redacted>

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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