On Wed, 11 Jan 2012 09:48:02 +0100
Michal Hocko <mhocko@xxxxxxx> wrote:
> On Tue 10-01-12 13:31:08, David Rientjes wrote:
> > On Tue, 10 Jan 2012, Michal Hocko wrote:
> [...]
> > > mm/page_alloc.c | 11 +++++++++++
> > > 1 files changed, 11 insertions(+), 0 deletions(-)
> > >
> > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > > index 2b8ba3a..485be89 100644
> > > --- a/mm/page_alloc.c
> > > +++ b/mm/page_alloc.c
> > > @@ -5608,6 +5608,17 @@ __count_immobile_pages(struct zone *zone, struct page *page, int count)
> > > bool is_pageblock_removable_nolock(struct page *page)
> > > {
> > > struct zone *zone = page_zone(page);
> > > + unsigned long pfn = page_to_pfn(page);
> > > +
Hmm, I don't like to use page_zone() when we know the page may not be initialized.
Shouldn't we add
if (!node_online(page_to_nid(page))
return false;
?
But...hmm. I think we should return 'true' here for removing a section with a hole
finally....(Now, false will be safe.)
> > > + /*
> > > + * We have to be careful here because we are iterating over memory
> > > + * sections which are not zone aware so we might end up outside of
> > > + * the zone but still within the section.
> > > + */
> > > + if (!zone || zone->zone_start_pfn > pfn ||
> > > + zone->zone_start_pfn + zone->spanned_pages <= pfn)
> > > + return false;
> > > +
> > > return __count_immobile_pages(zone, page, 0);
> > > }
> > >
> >
> > This seems partially bogus, why would
> >
> > page_zone(page)->zone_start_pfn > page_to_pfn(page) ||
> > page_zone(page)->zone_start_pfn + page_zone(page)->spanned_pages <= page_to_pfn(page)
> >
> > ever be true? That would certainly mean that the struct zone is corrupted
> > and seems to be unnecessary to fix the problem you're addressing.
>
> Not really. Consider the case when the node 0 is present. Uninitialized
> page would lead to node=0, zone=0 and then we have to check for the zone
> boundaries.
>
> > I think this should be handled in is_mem_section_removable() on the pfn
> > rather than using the struct page in is_pageblock_removable_nolock() and
> > converting back and forth. We should make sure that any page passed to
> > is_pageblock_removable_nolock() is valid.
>
> Yes, I do not like pfn->page->pfn dance as well and in fact I do not
> have a strong opinion which one is better. I just put it at the place
> where we care about zone to be more obvious. If others think that I
> should move the check one level higher I'll do that. I just think this
> is more obvious.
>
Hmm, mem_section and pageblock is a different chunk...
And, IIUC, in some IBM machines, section may includes several zones.
Please taking care of that if you move this to is_mem_section_removable()...
Thanks,
-Kame
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