Re: page fault fastpath: Increasing SMP scalability by introducing pte

[Manfred Spraul <manfred@colorfullife.com>]

Christoph wrote:

>Well this is more an idea than a real patch yet. The page_table_lock
>becomes a bottleneck if more than 4 CPUs are rapidly allocating and using
>memory. "pft" is a program that measures the performance of page faults on
>SMP system. It allocates memory simultaneously in multiple threads thereby
>causing lots of page faults for anonymous pages.
>
>  
>
Very odd. Why do you see a problem with the page_table_lock but no 
problem from the mmap semaphore?
The page fault codepath acquires both.
How often is the page table lock acquired per page fault? Just once or 
multiple spin_lock calls per page fault? Is the problem contention or 
cache line trashing?

Do you have profile/lockmeter output? Is the down_read() in 
do_page_fault() a hot spot, too?

--
    Manfred