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    SubjectRe: [PATCH v3] mm: simplify find_vma_prev
    >> Why have you removed this guard? Previously we had pprev==NULL and
    >> returned mm->mmap.
    >> This seems like a semantic change without any explanation. Could you
    >> clarify?
    > Scratch that. I have misread the code. find_vma will return mm->mmap if
    > the given address is bellow all vmas. Sorry about noise.
    > The only concern left would be the caching. Are you sure this will not
    > break some workloads which benefit from mmap_cache usage and would
    > interfere with find_vma_prev callers now? Anyway this could be fixed
    > trivially.

    Here is callers list.

    find_vma_prev 115 arch/ia64/mm/fault.c vma =
    find_vma_prev(mm, address, &prev_vma);
    find_vma_prev 183 arch/parisc/mm/fault.c vma =
    find_vma_prev(mm, address, &prev_vma);
    find_vma_prev 229 arch/tile/mm/hugetlbpage.c vma =
    find_vma_prev(mm, addr, &prev_vma);
    find_vma_prev 336 arch/x86/mm/hugetlbpage.c if
    (!(vma = find_vma_prev(mm, addr, &prev_vma)))
    find_vma_prev 388 mm/madvise.c vma =
    find_vma_prev(current->mm, start, &prev);
    find_vma_prev 642 mm/mempolicy.c vma = find_vma_prev(mm, start, &prev);
    find_vma_prev 388 mm/mlock.c vma =
    find_vma_prev(current->mm, start, &prev);
    find_vma_prev 265 mm/mprotect.c vma =
    find_vma_prev(current->mm, start, &prev);

    In short, find_find_prev() is only used from page fault, madvise, mbind, mlock
    and mprotect. And page fault is only performance impact callsite because other
    don't used frequently on regular workload.

    So, I wouldn't say, this patch has zero negative impact, but I think
    it is enough
    small and benefit is enough much.


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