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Date: Fri, 13 Oct 2017 14:07:56 +0200
From: Michal Hocko <mhocko@kernel.org>
Subject: Re: [PATCH 2/2] mm, page_alloc: fail has_unmovable_pages when seeing
 reserved pages
Message-ID: <20171013120756.jeopthigbmm3c7bl@dhcp22.suse.cz>
References: <20171013115835.zaehapuucuzl2vlv@dhcp22.suse.cz>
 <20171013120013.698-1-mhocko@kernel.org>
 <20171013120013.698-2-mhocko@kernel.org>
 <d98bfc90-e857-4bbe-bfbc-ee69dc310cc0@suse.cz>
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To: Vlastimil Babka <vbabka@suse.cz>
Cc: linux-mm@kvack.org, Michael Ellerman <mpe@ellerman.id.au>, Andrew Morton <akpm@linux-foundation.org>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, Reza Arbab <arbab@linux.vnet.ibm.com>, Yasuaki Ishimatsu <yasu.isimatu@gmail.com>, qiuxishi@huawei.com, Igor Mammedov <imammedo@redhat.com>, Vitaly Kuznetsov <vkuznets@redhat.com>, LKML <linux-kernel@vger.kernel.org>

On Fri 13-10-17 14:04:08, Vlastimil Babka wrote:
> On 10/13/2017 02:00 PM, Michal Hocko wrote:
> > From: Michal Hocko <mhocko@suse.com>
> > 
> > Reserved pages should be completely ignored by the core mm because they
> > have a special meaning for their owners. has_unmovable_pages doesn't
> > check those so we rely on other tests (reference count, or PageLRU) to
> > fail on such pages. Althought this happens to work it is safer to simply
> > check for those explicitly and do not rely on the owner of the page
> > to abuse those fields for special purposes.
> > 
> > Please note that this is more of a further fortification of the code
> > rahter than a fix of an existing issue.
> > 
> > Signed-off-by: Michal Hocko <mhocko@suse.com>
> > ---
> >  mm/page_alloc.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index ad0294ab3e4f..a8800b0a5619 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -7365,6 +7365,9 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
> >  
> >  		page = pfn_to_page(check);
> >  
> > +		if (PageReferenced(page))
> 
> "Referenced" != "Reserved"

Dohh, you are right of course. I blame auto-completion ;) but I am lame
in fact...
---