Messages in this thread | | | Subject | Re: [PATCH 1/4] mm: Trial do_wp_page() simplification | From | John Hubbard <> | Date | Thu, 17 Sep 2020 12:55:34 -0700 |
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On 9/17/20 12:42 PM, Linus Torvalds wrote: > On Thu, Sep 17, 2020 at 12:03 PM Peter Xu <peterx@redhat.com> wrote: ... > > Is there possibly somethign else we can filter on than just > GUP_PIN_COUNTING_BIAS? Because it could be as simple as just marking > the vma itself and saying "this vma has had a page pinning event done > on it". > > Because if we only start copying the page *iff* the vma is marked by > that "this vma had page pinning" _and_ the page count is bigger than > GUP_PIN_COUNTING_BIAS, than I think we can rest pretty easily knowing > that we aren't going to hit some regular old-fashioned UNIX server > cases with a lot of forks.. > > Linus
OK, so this sounds like an improvement that would be desirable in the core API:
1) Have all the pin_user_pages*() functions reach up and mark the vma(s) as FOLL_PIN_HAPPENED. I'm assuming that the vma can live it's full life without the need to ever clear that flag. That *seems* reasonable, based on the use cases for these kinds of pages.
2) And then rename:
page_maybe_dma_pinned() --> page_likely_dma_pinned()
:)
thanks, -- John Hubbard NVIDIA
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