You will NOT.
The page_table_lock protects against page stealing of the VM and
concurrent page-faults, nothing else. There is no way you can get
contention on it under any reasonable load that doesn't involve heavy
out-of-memory behaviour, simply because
- the lock is per-mm
- all "regular" paths that care about this also get the mmap semaphore
In short, that spinlock has _zero_ scalability impact. You can
theoretically get contention on it without memory pressure only by
having hundreds of threads page-faulting at the same time (getting a
read-lock on the mmap semaphore), but by then your performance has
nothing to do with the spinlock, and everything to do with the page
faults themselves.
(In fact, I can almost guarantee that most of the long hold-times are
for exit(), not for munmap(). And in that case the spinlock cannot get
any non-pagestealer contention at all, since nobody else is using the
MM)
Linus
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