Messages in this thread | | | Date | Thu, 28 May 2009 09:55:04 +0100 | From | Mel Gorman <> | Subject | Re: [PATCH 1/2] x86: Ignore VM_LOCKED when determining if hugetlb-backed page tables can be shared or not |
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On Thu, May 28, 2009 at 01:18:03AM +0200, Ingo Molnar wrote: > > * Mel Gorman <mel@csn.ul.ie> wrote: > > > On x86 and x86-64, it is possible that page tables are shared > > beween shared mappings backed by hugetlbfs. As part of this, > > page_table_shareable() checks a pair of vma->vm_flags and they > > must match if they are to be shared. All VMA flags are taken into > > account, including VM_LOCKED. > > > > The problem is that VM_LOCKED is cleared on fork(). When a process > > with a shared memory segment forks() to exec() a helper, there > > will be shared VMAs with different flags. The impact is that the > > shared segment is sometimes considered shareable and other times > > not, depending on what process is checking. > > > > What happens is that the segment page tables are being shared but > > the count is inaccurate depending on the ordering of events. As > > the page tables are freed with put_page(), bad pmd's are found > > when some of the children exit. The hugepage counters also get > > corrupted and the Total and Free count will no longer match even > > when all the hugepage-backed regions are freed. This requires a > > reboot of the machine to "fix". > > > > This patch addresses the problem by comparing all flags except > > VM_LOCKED when deciding if pagetables should be shared or not for > > hugetlbfs-backed mapping. > > > > Signed-off-by: Mel Gorman <mel@csn.ul.ie> > > Acked-by: Hugh Dickins <hugh.dickins@tiscali.co.uk> > > --- > > arch/x86/mm/hugetlbpage.c | 6 +++++- > > 1 files changed, 5 insertions(+), 1 deletions(-) > > i suspect it would be best to do this due -mm, due to the (larger) > mm/hugetlb.c cross section, right? >
I'm happy with that approach. Almost all hugetlbfs-related patches have gone through -mm to date AFAIK even when they have been arch specific like this.
Thanks
-- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab
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