Messages in this thread | | | Date | Sun, 2 Jul 2023 10:50:38 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH v7 0/6] Per-VMA lock support for swap and userfaults |
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On Fri, 30 Jun 2023 14:19:51 -0700 Suren Baghdasaryan <surenb@google.com> wrote:
> When per-VMA locks were introduced in [1] several types of page faults > would still fall back to mmap_lock to keep the patchset simple. Among them > are swap and userfault pages. The main reason for skipping those cases was > the fact that mmap_lock could be dropped while handling these faults and > that required additional logic to be implemented. > Implement the mechanism to allow per-VMA locks to be dropped for these > cases. > First, change handle_mm_fault to drop per-VMA locks when returning > VM_FAULT_RETRY or VM_FAULT_COMPLETED to be consistent with the way > mmap_lock is handled. Then change folio_lock_or_retry to accept vm_fault > and return vm_fault_t which simplifies later patches. Finally allow swap > and uffd page faults to be handled under per-VMA locks by dropping per-VMA > and retrying, the same way it's done under mmap_lock. > Naturally, once VMA lock is dropped that VMA should be assumed unstable > and can't be used.
Is there any measurable performance benefit from this?
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