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

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Message-Id: <20070611183555.fe763fe4.akpm@linux-foundation.org>
Date:	Mon, 11 Jun 2007 18:35:55 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Arjan van de Ven <arjan@...ux.intel.com>
Cc:	"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, 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.

I don't see why it is better to consume the reserves before going to the
page allocator instead of holding them, err, in reserve.

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