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    SubjectRe: [PATCH 1/5] freepgt: free_pgtables use vma list
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    On Tue, 2005-03-22 at 16:37 +0000, Hugh Dickins wrote:
    > On Tue, 22 Mar 2005, Andrew Morton wrote:
    > >
    > > With these six patches the ppc64 is hitting the BUG in exit_mmap():
    > >
    > > BUG_ON(mm->nr_ptes); /* This is just debugging */
    > >
    > > fairly early in boot.
    >
    > So ppc64 is in the same boat as sparc64 (yet ia64 okay so far).
    >
    > Sorry, I'm still clueless.
    >
    > I cannot see those arches doing pte_allocs outside their vmas,
    > that of course could cause it. And nr_ptes is initialized to 0
    > once by memset and again by assignment, so it should be starting
    > out even zeroer than most fields.

    We do funny things in arch/ppc64/mm/init.c in the ioremap_mm, where we
    don't use VMAs but our own mecanism (yah, ugly, but that's some legacy
    we have from the original port, though I do intend to change that at one
    point).

    > I should probably be paying more attention to the repellent
    > notion that my code is broken.
    >
    > If you and David could try the lame patch below,
    > it'll at least give us a slight clue of where to be looking -
    > every mm exiting with nr_ptes 1 means something different from
    > every mm exiting with nr_ptes -1 means something different from
    > occasional mms exiting with nr_ptes something positive.
    >
    > I'm not sure whether the patch would ever get to show a more
    > interesting proc name than "?".
    >
    > And does memory leak away into lost pagetables if you continue
    > running, or does it actually carry on running fine, and the
    > problem appear to be with the BUG_ON itself?
    >
    > Thanks,
    > Hugh
    >
    > --- freepgt6/mm/mmap.c 2005-03-22 04:28:40.000000000 +0000
    > +++ testing/mm/mmap.c 2005-03-22 15:45:00.000000000 +0000
    > @@ -1896,6 +1896,7 @@ EXPORT_SYMBOL(do_brk);
    > /* Release all mmaps. */
    > void exit_mmap(struct mm_struct *mm)
    > {
    > + static unsigned long good_mms, bad_mms;
    > struct mmu_gather *tlb;
    > struct vm_area_struct *vma = mm->mmap;
    > unsigned long nr_accounted = 0;
    > @@ -1931,7 +1932,14 @@ void exit_mmap(struct mm_struct *mm)
    > vma = next;
    > }
    >
    > - BUG_ON(mm->nr_ptes); /* This is just debugging */
    > + if (mm->nr_ptes && bad_mms < 250) {
    > + printk(KERN_ERR "exit_mmap: %s nr_ptes %ld good_mms %lu\n",
    > + current->mm == mm? current->comm: "?",
    > + (long)mm->nr_ptes, good_mms);
    > + good_mms = 0;
    > + bad_mms++;
    > + } else
    > + good_mms++;
    > }
    >
    > /* Insert vm structure into process list sorted by address
    --
    Benjamin Herrenschmidt <benh@kernel.crashing.org>

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