linux-kernel - Re: [PATCH] memcgroup: check and initialize page->cgroup in memmap_init

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Date:	Fri, 18 Apr 2008 12:32:56 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Shi Weihua <shiwh@...fujitsu.com>, balbir@...ux.vnet.ibm.com,
	xemul@...nvz.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	hugh@...itas.com
Subject: Re: [PATCH] memcgroup: check and initialize page->cgroup in
 memmap_init_zone

On Thu, 17 Apr 2008 20:14:32 -0700
Andrew Morton <akpm@...ux-foundation.org> wrote:

> >  	for (pfn = start_pfn; pfn < end_pfn; pfn++) {
> >  		/*
> > @@ -2535,6 +2536,9 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
> >  		set_page_links(page, zone, nid, pfn);
> >  		init_page_count(page);
> >  		reset_page_mapcount(page);
> > +		pc = page_get_page_cgroup(page);
> > +		if (pc) 
> > +			page_reset_bad_cgroup(page);
> >  		SetPageReserved(page);
> >  
> 
> hm, fishy.  Perhaps the architecture isn't zeroing the memmap arrays?
> 
AFAIK, No. memmap is allocated by alloc_bootmem() and returned memory is
cleared by memset().

> Or perhaps that page was used and then later freed before we got to
> memmap_init_zone() and was freed with a non-zero ->page_cgroup.  Which is
> unlikely given that page.page_cgroup was only just added and is only
> present if CONFIG_CGROUP_MEM_RES_CTLR.
> 
Hmm, I'll try his .config and see what happens.

Thanks,
-Kame

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