netdev - RE: [PATCH] percpu: add optimized generic percpu accessors

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Date:	Wed, 28 Jan 2009 11:48:27 -0500 (EST)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	"Luck, Tony" <tony.luck@...el.com>
cc:	Rick Jones <rick.jones2@...com>,
	David Miller <davem@...emloft.net>,
	"tj@...nel.org" <tj@...nel.org>,
	"rusty@...tcorp.com.au" <rusty@...tcorp.com.au>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"hpa@...or.com" <hpa@...or.com>,
	"brgerst@...il.com" <brgerst@...il.com>,
	"ebiederm@...ssion.com" <ebiederm@...ssion.com>,
	"travis@....com" <travis@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"steiner@....com" <steiner@....com>,
	"hugh@...itas.com" <hugh@...itas.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"mathieu.desnoyers@...ymtl.ca" <mathieu.desnoyers@...ymtl.ca>,
	"linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>
Subject: RE: [PATCH] percpu: add optimized generic percpu accessors

On Tue, 27 Jan 2009, Luck, Tony wrote:

> Managing a larger space could be done ... but at the expense of making
> the Alt-DTLB miss handler do a memory lookup to find the physical address
> of the per-cpu page needed (assuming that we allocate a bunch of random
> physical pages for use as per-cpu space rather than a single contiguous
> block of physical memory).

We cannot resize the area by using a single larger TLB entry?

> When do we know the total amount of per-cpu memory needed?
> 1) CONFIG time?

Would be easiest.

> 2) Boot time?

We could make the TLB entry size configurable with a kernel parameter

> 3) Arbitrary run time?

We could reserve a larger virtual space and switch TLB entries as needed?
We would need do get larger order pages to do this.

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