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    SubjectRe: [PATCH -V9 04/15] hugetlb: use mmu_gather instead of a temporary linked list for accumulating pages
    On Wed 13-06-12 15:57:23, Aneesh Kumar K.V wrote:
    > From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
    >
    > Use a mmu_gather instead of a temporary linked list for accumulating
    > pages when we unmap a hugepage range

    Sorry for coming up with the comment that late but you owe us an
    explanation _why_ you are doing this.

    I assume that this fixes a real problem when we take i_mmap_mutex
    already up in
    unmap_mapping_range
    mutex_lock(&mapping->i_mmap_mutex);
    unmap_mapping_range_tree | unmap_mapping_range_list
    unmap_mapping_range_vma
    zap_page_range_single
    unmap_single_vma
    unmap_hugepage_range
    mutex_lock(&vma->vm_file->f_mapping->i_mmap_mutex);

    And that this should have been marked for stable as well (I haven't
    checked when this has been introduced).

    But then I do not see how this help when you still do this:
    [...]
    > diff --git a/mm/memory.c b/mm/memory.c
    > index 1b7dc66..545e18a 100644
    > --- a/mm/memory.c
    > +++ b/mm/memory.c
    > @@ -1326,8 +1326,11 @@ static void unmap_single_vma(struct mmu_gather *tlb,
    > * Since no pte has actually been setup, it is
    > * safe to do nothing in this case.
    > */
    > - if (vma->vm_file)
    > - unmap_hugepage_range(vma, start, end, NULL);
    > + if (vma->vm_file) {
    > + mutex_lock(&vma->vm_file->f_mapping->i_mmap_mutex);
    > + __unmap_hugepage_range(tlb, vma, start, end, NULL);
    > + mutex_unlock(&vma->vm_file->f_mapping->i_mmap_mutex);
    > + }
    > } else
    > unmap_page_range(tlb, vma, start, end, details);
    > }

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


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