linux-kernel - Re: [PATCH v2 2/2] xen/setup: Remap Xen Identity Mapped RAM

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Date:	Tue, 26 Aug 2014 13:40:09 -0700
From:	Matthew Rushton <mvrushton@...il.com>
To:	David Vrabel <david.vrabel@...rix.com>, konrad.wilk@...cle.com,
	boris.ostrovsky@...cle.com
CC:	msw@...zon.com, linux-kernel@...r.kernel.org,
	xen-devel@...ts.xensource.com, Matt Rushton <mrushton@...zon.com>
Subject: Re: [PATCH v2 2/2] xen/setup: Remap Xen Identity Mapped RAM

On 08/01/14 07:52, David Vrabel wrote:
> On 31/07/14 18:43, David Vrabel wrote:
>> On 20/07/14 01:01, Matt Rushton wrote:
>>> Instead of ballooning up and down dom0 memory this remaps the existing mfns
>>> that were replaced by the identity map. The reason for this is that the
>>> existing implementation ballooned memory up and and down which caused dom0
>>> to have discontiguous pages. In some cases this resulted in the use of bounce
>>> buffers which reduced network I/O performance significantly. This change will
>>> honor the existing order of the pages with the exception of some boundary
>>> conditions.
>>>
>>> To do this we need to update both the Linux p2m table and the Xen m2p table.
>>> Particular care must be taken when updating the p2m table since it's important
>>> to limit table memory consumption and reuse the existing leaf pages which get
>>> freed when an entire leaf page is set to the identity map. To implement this,
>>> mapping updates are grouped into blocks with table entries getting cached
>>> temporarily and then released.
>>>
>>> On my test system before:
>>> Total pages: 2105014
>>> Total contiguous: 1640635
>>>
>>> After:
>>> Total pages: 2105014
>>> Total contiguous: 2098904
>> Applied to devel/for-linus-3.17
> Unfortunately, this produces too many WARNINGs on some boxes or
> with certain configurations.
>
> I will remove this patch from the queue for 3.17.
>

Have you had a chance to try the v3 patch set?


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