On Mon, 6 Jun 2011 14:45:19 -0700
Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Mon, 6 Jun 2011 14:54:21 +0200
> Johannes Weiner <hannes@xxxxxxxxxxx> wrote:
>
> > Cc Mel for memory model
> >
> > On Mon, May 30, 2011 at 05:51:40PM +0900, KAMEZAWA Hiroyuki wrote:
> > > On Mon, 30 May 2011 16:54:53 +0900
> > > KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
> > >
> > > > On Mon, 30 May 2011 16:29:04 +0900
> > > > KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
> > >
> > > > SRAT: Node 1 PXM 1 0-a0000
> > > > SRAT: Node 1 PXM 1 100000-c8000000
> > > > SRAT: Node 1 PXM 1 100000000-438000000
> > > > SRAT: Node 3 PXM 3 438000000-838000000
> > > > SRAT: Node 5 PXM 5 838000000-c38000000
> > > > SRAT: Node 7 PXM 7 c38000000-1038000000
> > > >
> > > > Initmem setup node 1 0000000000000000-0000000438000000
> > > > NODE_DATA [0000000437fd9000 - 0000000437ffffff]
> > > > Initmem setup node 3 0000000438000000-0000000838000000
> > > > NODE_DATA [0000000837fd9000 - 0000000837ffffff]
> > > > Initmem setup node 5 0000000838000000-0000000c38000000
> > > > NODE_DATA [0000000c37fd9000 - 0000000c37ffffff]
> > > > Initmem setup node 7 0000000c38000000-0000001038000000
> > > > NODE_DATA [0000001037fd7000 - 0000001037ffdfff]
> > > > [ffffea000ec40000-ffffea000edfffff] potential offnode page_structs
> > > > [ffffea001cc40000-ffffea001cdfffff] potential offnode page_structs
> > > > [ffffea002ac40000-ffffea002adfffff] potential offnode page_structs
> > > > ==
> > > >
> > > > Hmm..there are four nodes 1,3,5,7 but....no memory on node 0 hmm ?
> > > >
> > >
> > > I think I found a reason and this is a possible fix. But need to be tested.
> > > And suggestion for better fix rather than this band-aid is appreciated.
> > >
> > > ==
> > > >From b95edcf43619312f72895476c3e6ef46079bb05f Mon Sep 17 00:00:00 2001
> > > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> > > Date: Mon, 30 May 2011 16:49:59 +0900
> > > Subject: [PATCH][BUGFIX] fallbacks at page_cgroup allocation.
> > >
> > > Under SPARSEMEM, the page_struct is allocated per section.
> > > Then, pfn_valid() for the whole section is "true" and there are page
> > > structs. But, it's not related to valid range of [start_pfn, end_pfn)
> > > and some page structs may not be initialized collectly because
> > > it's not a valid pages.
> > > (memmap_init_zone() skips a page which is not correct in
> > > early_node_map[] and page->flags is initialized to be 0.)
> > >
> > > In this case, a page->flags can be '0'. Assume a case where
> > > node 0 has no memory....
> > >
> > > page_cgroup is allocated onto the node
> > >
> > > - page_to_nid(head of section pfn)
> > >
> > > Head's pfn will be valid (struct page exists) but page->flags is 0 and contains
> > > node_id:0. This causes allocation onto NODE_DATA(0) and cause panic.
> > >
> > > This patch makes page_cgroup to use alloc_pages_exact() only
> > > when NID is N_NORMAL_MEMORY.
>
> fyi, the reporter has gone in via the bugzilla UI and says he has
> tested the patch and it worked well.
>
> Please don't do that! See this?
>
> : (switched to email. Please respond via emailed reply-to-all, not via the
> : bugzilla web interface).
>
> So we have a tested-by if we use this patch.
>
> > I don't like this much as it essentially will allocate the array from
> > a (semantically) random node, as long as it has memory.
> >
> > IMO, the problem is either 1) looking at PFNs outside known node
> > ranges, or 2) having present/valid sections partially outside of node
> > ranges. I am leaning towards 2), so I am wondering about the
> > following fix:
> >
> > ---
> > From: Johannes Weiner <hannes@xxxxxxxxxxx>
> > Subject: [patch] sparse: only mark sections present when fully covered by memory
> >
> > When valid memory ranges are to be registered with sparsemem, make
> > sure that only fully covered sections are marked as present.
> >
> > Otherwise we end up with PFN ranges that are reported present and
> > valid but are actually backed by uninitialized mem map.
> >
> > The page_cgroup allocator relies on pfn_present() being reliable for
> > all PFNs between 0 and max_pfn, then retrieve the node id stored in
> > the corresponding page->flags to allocate the per-section page_cgroup
> > arrays on the local node.
> >
> > This lead to at least one crash in the page allocator on a system
> > where the uninitialized page struct returned the id for node 0, which
> > had no memory itself.
> >
> > Reported-by: qcui@xxxxxxxxxx
> > Debugged-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> > Not-Yet-Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> > ---
> >
> > diff --git a/mm/sparse.c b/mm/sparse.c
> > index aa64b12..a4fbeb8 100644
> > --- a/mm/sparse.c
> > +++ b/mm/sparse.c
> > @@ -182,7 +182,9 @@ void __init memory_present(int nid, unsigned long start, unsigned long end)
> > {
> > unsigned long pfn;
> >
> > - start &= PAGE_SECTION_MASK;
> > + start = ALIGN(start, PAGES_PER_SECTION);
> > + end &= PAGE_SECTION_MASK;
> > +
> > mminit_validate_memmodel_limits(&start, &end);
> > for (pfn = start; pfn < end; pfn += PAGES_PER_SECTION) {
> > unsigned long section = pfn_to_section_nr(pfn);
> >
>
> Hopefully he can test this one for us as well, thanks.
>
My concern is ARM. I know ARM unmaps 'struct page' even if pages are in
existing section.
So, I wonder above fix may cause a new panic at boot with ARM.
Then, I used a dirty hack ;)
But I'm not sure. ARM is too special at memmap handling.
I think this Johannes's patch should be tested by ARM (and possiblye all arch)
before merge.
Thanks,
-Kame
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxxx For more info on Linux MM,
see: http://www.linux-mm.org/ .
Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>