Messages in this thread | | | Date | Thu, 16 Jul 2020 16:16:12 +0300 | From | "Kirill A. Shutemov" <> | Subject | Re: [PATCHv2] mm: Fix warning in move_normal_pmd() |
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On Wed, Jul 15, 2020 at 04:18:44PM -0700, Linus Torvalds wrote: > On Wed, Jul 15, 2020 at 4:04 PM Linus Torvalds > <torvalds@linux-foundation.org> wrote: > > > > It *might* be as simple as this incremental thing on top > > No, it needs to be > > + if (*old_addr + *len < old->vm_end) > + return; > > in try_to_align_end(), of course.
Okay, this should work, but I'm not convinced that it gives much: number of cases covered by the optimization not going to be high.
It can also lead to performance regression: for small mremap() if only one side of the range got aligned and there's no PMD_SIZE range to move, kernel will still iterate over PTEs, but it would need to handle more pte_none()s than without the patch.
-- Kirill A. Shutemov
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