Re: [Xen-devel] writable pagetables scalability issue

[Rik van Riel <riel@xxxxxxxxxx>]

On Fri, 07 Dec 2007 17:47:40 +0000
Keir Fraser <Keir.Fraser@xxxxxxxxxxxx> wrote:

> On 7/12/07 17:06, "Rik van Riel" <riel@xxxxxxxxxx> wrote:
> 
> > Does anybody see issues with putting all of the writable pagetable
> > operations under a read-write lock, with the code paths that change
> > page table entries (mostly the fault handling) taking the lock in
> > read mode, and the code paths that change the status of pages taking
> > the lock in write mode?
> > 
> > That way we can guarantee that the writable page table pages do not
> > change status while handling a fault (and we get concurrency), blocking
> > out the write fault handling only while new page table pages are being
> > created or destroyed.
> 
> I think we can probably just as easily strip out the big lock entirely from
> the critical paths. It's not really needed much these days.

"not needed much" makes me kind of nervous :)

Exactly what do we still need to protect against?

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