On Thu, 12 Jan 2012 10:23:14 +0100
Michal Hocko <mhocko@xxxxxxx> wrote:
> On Thu 12-01-12 17:35:36, KAMEZAWA Hiroyuki wrote:
> > On Thu, 12 Jan 2012 09:27:22 +0100
> > Michal Hocko <mhocko@xxxxxxx> wrote:
> >
> > > On Thu 12-01-12 11:17:02, KAMEZAWA Hiroyuki wrote:
> > > > 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;
> > > > ?
> > >
> > > How is this different? The node won't be initialized in page flags as
> > > well.
> > >
> >
> > page_zone(page) is
> > ==
> > static inline struct zone *page_zone(const struct page *page)
> > {
> > return &NODE_DATA(page_to_nid(page))->node_zones[page_zonenum(page)];
> > }
> > ==
> >
> > Then, if the page is unitialized,
> >
> > &(NODE_DATA(0)->node_zones[0])
> >
> > If NODE_DATA(0) is NULL, node_zones[0] is NULL just because zone array is placed
> > on the top of struct pglist_data.
> >
> > I never think someone may change the layout but...Hmm, just a nitpick.
> > please do as you like.
>
> Yes, fair point. See the follow up patch bellow.
>
> > > > But...hmm. I think we should return 'true' here for removing a section with a hole
> > > > finally....(Now, false will be safe.)
> > >
> > > Those pages are reserved (for BIOS I guess) in this particular case so I
> > > do not think it is safe to claim that the block is removable. Or am I
> > > missing something?
> > >
> >
> > We can't know it's reserved by BIOS or it's just a memory hole by the fact
> > the page wasn't initialized.
>
> OK, so then we should return false to mark to block non removable,
> right?
Ok.
> ---
> From 04f74e6f0ebf28f61650d63f8884e8855fb21b55 Mon Sep 17 00:00:00 2001
> From: Michal Hocko <mhocko@xxxxxxx>
> Date: Thu, 12 Jan 2012 10:19:04 +0100
> Subject: [PATCH] mm: __count_immobile_pages make sure the node is online
>
> page_zone requires to have an online node otherwise we are accessing
> NULL NODE_DATA. This is not an issue at the moment because node_zones
> are located at the structure beginning but this might change in the
> future so better be careful about that.
>
> Signed-off-by: Michal Hocko <mhocko@xxxxxxx>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> ---
> mm/page_alloc.c | 11 +++++++++--
> 1 files changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 485be89..c6fb8ea 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5607,14 +5607,21 @@ __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);
> + struct zone *zone;
> + unsigned long pfn;
>
> /*
> * 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.
> + * We have to take care about the node as well. If the node is offline
> + * its NODE_DATA will be NULL - see page_zone.
> */
> + if (!node_online(page_to_nid(page)))
> + return false;
> +
> + zone = page_zone(page);
> + pfn = page_to_pfn(page);
> if (!zone || zone->zone_start_pfn > pfn ||
> zone->zone_start_pfn + zone->spanned_pages <= pfn)
> return false;
!zone check can be removed because of node_online() check.
Thanks,
-Kame
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