Re: [PATCH 2/2] mm, page_alloc: fail has_unmovable_pages when seeing reserved pages

[Michal Hocko]

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@xxxxxxxx>
> > 
> > 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@xxxxxxxx>
> > ---
> >  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...
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