linux-kernel - Re: [patch 0/7] [RFC] SLUB: Improve allocpercpu to reduce per cpu access overhead

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Date:	Thu, 1 Nov 2007 17:58:49 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Eric Dumazet <dada1@...mosbay.com>
cc:	David Miller <davem@...emloft.net>, akpm@...ux-foundation.org,
	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
	mathieu.desnoyers@...ymtl.ca, penberg@...helsinki.fi
Subject: Re: [patch 0/7] [RFC] SLUB: Improve allocpercpu to reduce per cpu
 access overhead

On Fri, 2 Nov 2007, Eric Dumazet wrote:

> > Na. Some reasonable upper limit needs to be set. If we set that to say
> > 32Megabytes and do the virtual mapping then we can just populate the first
> > 2M and only allocate the remainder if we need it. Then we need to rely on
> > Mel's defrag stuff though defrag memory if we need it.
> 
> If a 2MB page is not available, could we revert using 4KB pages ? (like
> vmalloc stuff), paying an extra runtime overhead of course.

Sure. Its going to be like vmemmap. There will be limited imposed though 
by the amount of virtual space available. Basically the dynamic per cpu 
area can be at maximum

available_virtual_space / NR_CPUS

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