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Re: [Xen-devel] Xen 4.0.1 "xc_map_foreign_batch: mmap failed: Cannot a

To: Jan Beulich <JBeulich@xxxxxxxxxx>
Subject: Re: [Xen-devel] Xen 4.0.1 "xc_map_foreign_batch: mmap failed: Cannot allocate memory"
From: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Date: Wed, 5 Jan 2011 17:48:06 +0000
Cc: Arnold <CARNOLD@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Keir Fraser <keir@xxxxxxx>, Charles, Stefano Stabellini <Stefano.Stabellini@xxxxxxxxxxxxx>
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References: <C9302D00.D25D%keir@xxxxxxx> <alpine.DEB.2.00.1101051422360.2390@kaball-desktop> <4D249CBD020000780002A7E4@xxxxxxxxxxxxxxxxxx> <alpine.DEB.2.00.1101051601440.2390@kaball-desktop> <4D24AB7E020000780002A861@xxxxxxxxxxxxxxxxxx>
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User-agent: Alpine 2.00 (DEB 1167 2008-08-23)
On Wed, 5 Jan 2011, Jan Beulich wrote:
> But this means it can have very close to the total amount of
> memory the guest has in flight on its own. Clearly this should
> be throttled based on available memory (just consider you have
> multiple such I/O hungry guests).

This is true in theory, but Qemu emulates a PIIX3 chipset that only has
two dma engines so I don't believe is possible to have more than 2 dma
requests in flight.
However I am not sure what is the maximum size for a single dma request.

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