linux-kernel - Re: [mmotm] BUG: Bad page state in process khugepaged ?

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Date:	Wed, 9 Feb 2011 21:07:28 +0100
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"hannes@...xchg.org" <hannes@...xchg.org>
Subject: Re: [mmotm] BUG: Bad page state in process khugepaged ?

On Wed, Feb 09, 2011 at 03:52:46PM +0900, KAMEZAWA Hiroyuki wrote:
> On Wed, 9 Feb 2011 15:50:01 +0900
> Daisuke Nishimura <nishimura@....nes.nec.co.jp> wrote:
> 
> > > 
> > > In hex, pc->flags was 7A00000000004 and this means PCG_USED bit is set.
> > > This implies page_remove_rmap() may not be called but ->mapping is NULL. Hmm?
> > > (7A is encoding of section number.)
> > > 
> > Sigh.. it seems another freed-but-not-uncharged problem..
> > 
> 
> Ah, ok, this is maybe caused by this. I'm sorry that I missed this.
> ==
> static inline int free_pages_check(struct page *page)
> {
>         if (unlikely(page_mapcount(page) |
>                 (page->mapping != NULL)  |
>                 (atomic_read(&page->_count) != 0) |
>                 (page->flags & PAGE_FLAGS_CHECK_AT_FREE) |
>                 (mem_cgroup_bad_page_check(page)))) {    <==========(*)
>                 bad_page(page);
>                 return 1;
> ==
> 
> Then, ok, this is a memcgroup and hugepage issue.
> 
> I'll look into.

Yes, the rest of the info on the page looked ok and shouldn't have
triggered a bad_page call. Thanks so much for looking into it.

Andrea
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