On Mon, Dec 21, 2020 at 03:33:30PM -0800, Linus Torvalds wrote:
On Mon, Dec 21, 2020 at 3:12 PM Yu Zhao yuzhao@google.com wrote:
I can't say I disagree with you but the man has made the call and I think we should just move on.
"The man" can always be convinced by numbers.
So if somebody comes up with an alternate patch, and explains it, and shows that it is better - go for it.
I just think that if mprotect() can take the mmap lock for writing, then userfaultfd sure as hell can. What odd load does people have where userfaultfd is more important than mprotect?
So as far as the man is concerned, I think "just fix userfaultfd" is simply the default obvious operation.
Not necessarily a final endpoint.
Linus
My first instinct is to be conservative and revert 09854ba94c6a ("mm: do_wp_page() simplification") so people are less likely to come back and complain about performance issues from holding mmap lock for write when clearing pte_write.
That being said, I do like the simplicity of 09854ba94c6a as well as having one simple rule that dictates what we should do when clearing pte_write(). And "userfaultfd is not the most important part of the system" is a fair point.