Re: page fault fastpath: Increasing SMP scalability by introducingpte

[Manfred Spraul]

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
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