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?
---
>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;
--
1.7.7.3
--
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9
Czech Republic
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