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SubjectRe: [PATCH 2/4 v0.5] sched/umcg: RFC: add userspace atomic helpers
On Wed, Sep 15, 2021 at 09:50:41AM -0700, Andy Lutomirski wrote:
> What's the precise problem? The code would be roughly:
>
> if (try_pin_the_page) {
> write it;
> unpin;
> } else {
> do nothing -- .fault will fill in the correct contents.
> }
>
> The time this takes is nondeterministic, but it's bounded and short.

You can't do this from sched_submit_work(), you might already hold
mmap_sem. Hence the suggestion to, for UMCG registered threads, pin the
page(s) on syscall-enter and unpin on either schedule() or
syscall-return.

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