Re: [RFC][PATCH 6/8] mm: handle_speculative_fault()

[Andi Kleen]

Arjan van de Ven <arjan@xxxxxxxxxxxxx> writes:

> On Mon, 04 Jan 2010 19:24:35 +0100
> Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> wrote:
>
>> Generic speculative fault handler, tries to service a pagefault
>> without holding mmap_sem.
>
>
> while I appreciate the goal of reducing contention on this lock...
> wouldn't step one be to remove the page zeroing from under this lock?
> that's by far (easily by 10x I would guess) the most expensive thing
> that's done under the lock, and I would expect a first order of
> contention reduction just by having the zeroing of a page not done
> under the lock...

The cache line bouncing of the shared cache lines hurts too.

I suspect fixing this all properly will need some deeper changes.

-Andi
-- 
ak@xxxxxxxxxxxxxxx -- Speaking for myself only.
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