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

[William Lee Irwin III <wli@holomorphy.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.

On Sun, Aug 15, 2004 at 04:17:11PM +0200, Manfred Spraul wrote:
> 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?

->mmap_sem would likely be useful to address as well. A different
structure for vma trees, more amenable to finegrained locking or
lockfree algorithms, would likely be useful there.


-- wli