On Tue, 7 Jun 2011 09:45:30 +0100
Mel Gorman <mgorman@xxxxxxx> wrote:
> On Tue, Jun 07, 2011 at 08:45:30AM +0900, KAMEZAWA Hiroyuki wrote:
> > 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.
>
> Yes, but not outside zone boundaries. The problem for ARM is having
> zones unaligned to sections. The struct pages for the non-resident
> memory gets unmapped. This is a problem for linear PFN walkers that
> align to boundaries unrelated to the zone such as to MAX_ORDER_NR_PAGES
> or pageblock_nr_pages.
>
zone boundary is not problem. If memmap for head of section is unmapped and
reused, we'll see wrong node because page->flags is broken.
Thanks,
-Kame
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