From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [PATCH for 4.7] xen: Replace
 alloc_vcpu_guest_context() with vmalloc()
Date: Fri, 21 Aug 2015 19:10:51 +0100
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To: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Ian Campbell <ian.campbell@citrix.com>, Tim Deegan <tim@xen.org>, Xen-devel <xen-devel@lists.xen.org>, Stefano Stabellini <stefano.stabellini@citrix.com>, Jan Beulich <JBeulich@suse.com>, Roger Pau Monne <roger.pau@citrix.com>
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On 21/08/15 18:55, Konrad Rzeszutek Wilk wrote:
> On Fri, Aug 21, 2015 at 06:51:46PM +0100, Andrew Cooper wrote:
>> This essentially reverts c/s 2037f2adb "x86: introduce
>> alloc_vcpu_guest_context()", including the newer arm bits, but achieves
>> the same end goal by using the newer vmalloc() infrastructure.
> Could you explain what this fixes? Or perhaps with an explanation
> of why this will make Xen [ ]better; [ ] faster [ ] magical.
>
> :-)

Ain't the diffstat enough to qualify for [x]better ;) ?

>
>
> Thanks.

It is relevant to a patch of Rogers which I am reviewing from the no-DM
series.  I was writing in reply to that, but this can also do.

alloc_vcpu_guest_context() was introduced long before vmalloc(), and
attempts to make the same end result using per-pcpu fixmap entries,
which scale by the compile-time NR_CPUS.

This patch causes a net reduction in compiled size for each arch (small
for ARM, larger for x86) and removes a scalability limit for compiling
with large numbers of cpus.

I think I can guess what you are going to ask me to do, given this
explanation.

~Andrew