Re: [RFC][PATCH 4/6] SRCU free VMAs

[Christoph Lameter]

On Fri, 24 Oct 2014, Peter Zijlstra wrote:

> The hold time isn't relevant, in fact breaking up the mmap_sem such that
> we require multiple acquisitions will just increase the cacheline
> bouncing.

Well this wont be happening anymore once you RCUify the stuff. If you go
to sleep then its best to release mmap_sem and then the bouncing wont
matter.

Dropping mmap_sem there will also expose you to races you will see later
too when you RCUify the code paths. That way those can be deal with
beforehand.

> Also I think it makes more sense to continue an entire fault operation,
> including blocking, if at all possible. Every retry will just waste more
> time.

Ok then dont retry. Just drop mmap_sem before going to sleep. When you
come back evaluate the situation and if we can proceed do so otherwise
retry.
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