Re: [PATCH 2/4 v0.5] sched/umcg: RFC: add userspace atomic helpers
From: Peter Zijlstra <peterz@infradead.org>
Date: 2021-09-15 19:12:39
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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.