linux-kernel - Re: [PATCH 09/10] percpu: implement new dynamic percpu allocator

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Message-Id: <200902192336.02800.nickpiggin@yahoo.com.au>
Date:	Thu, 19 Feb 2009 23:36:01 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Tejun Heo <tj@...nel.org>
Cc:	rusty@...tcorp.com.au, tglx@...utronix.de, x86@...nel.org,
	linux-kernel@...r.kernel.org, hpa@...or.com, jeremy@...p.org,
	cpw@....com, mingo@...e.hu
Subject: Re: [PATCH 09/10] percpu: implement new dynamic percpu allocator

On Wednesday 18 February 2009 23:04:35 Tejun Heo wrote:
> Impact: new scalable dynamic percpu allocator which allows dynamic
>         percpu areas to be accessed the same way as static ones
>
> Implement scalable dynamic percpu allocator which can be used for both
> static and dynamic percpu areas.  This will allow static and dynamic
> areas to share faster direct access methods.  This feature is optional
> and enabled only when CONFIG_HAVE_DYNAMIC_PER_CPU_AREA is defined by
> arch.  Please read comment on top of mm/percpu.c for details.

Seems pretty nice. Wishlist: would be cool to have per-cpu virtual
memory mappings and do CPU-local percpu access via a single pointer.
Of course there would need to be some machinery and maybe a new API
to be more careful about accessing remote percpu data (that access
could perhaps just be slower and go via the linear mapping).

It would probably be quite a bit slower to do remote percpu access,
but some users never do this remote access in fastpath, and want
really fast local access (eg slab allocators).

I guess the hardest part would be doing the arch code.

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