linux-kernel - Re: [Intel-IOMMU 02/10] Library routine for pre-allocat pool handling

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Message-ID: <20070613184011.GK11166@waste.org>
Date:	Wed, 13 Jun 2007 13:40:11 -0500
From:	Matt Mackall <mpm@...enic.com>
To:	Arjan van de Ven <arjan@...ux.intel.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Keshavamurthy, Anil S" <anil.s.keshavamurthy@...el.com>,
	Andi Kleen <ak@...e.de>, Christoph Lameter <clameter@....com>,
	linux-kernel@...r.kernel.org, gregkh@...e.de, muli@...ibm.com,
	asit.k.mallick@...el.com, suresh.b.siddha@...el.com,
	ashok.raj@...el.com, shaohua.li@...el.com, davem@...emloft.net
Subject: Re: [Intel-IOMMU 02/10] Library routine for pre-allocat pool handling

On Mon, Jun 11, 2007 at 06:55:46PM -0700, Arjan van de Ven wrote:
> Andrew Morton wrote:
> >On Mon, 11 Jun 2007 18:10:40 -0700 Arjan van de Ven 
> ><arjan@...ux.intel.com> wrote:
> >
> >>Andrew Morton wrote:
> >>>>Where as resource pool is exactly opposite of mempool, where each 
> >>>>time it looks for an object in the pool and if it exist then we 
> >>>>return that object else we try to get the memory for OS while 
> >>>>scheduling the work to grow the pool objects. In fact, the  work
> >>>>is schedule to grow the pool when the low threshold point is hit.
> >>>I realise all that.  But I'd have thought that the mempool approach is
> >>>actually better: use the page allocator and only deplete your reserve 
> >>>pool
> >>>when the page allocator fails.
> >>the problem with that is that if anything downstream from the iommu 
> >>layer ALSO needs memory, we've now eaten up the last free page and 
> >>things go splat.
> >
> >If that happens, we still have the mempool reserve to fall back to.
> 
> we do, except that we just ate the memory the downstream code would 
> use and get ... so THAT can't get any.

Then the downstream ought to be using a mempool?

-- 
Mathematics is the supreme nostalgia of our time.
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