linux-kernel - Re: [RFC 0/2] kvm: Transcendent Memory (tmem) on KVM

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Message-ID: <4F621FC0.7050800@redhat.com>
Date:	Thu, 15 Mar 2012 18:58:40 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Akshay Karle <akshay.a.karle@...il.com>
CC:	linux-kernel@...r.kernel.org,
	Dan Magenheimer <dan.magenheimer@...cle.com>,
	konrad.wilk@...cle.com, kvm@...r.kernel.org,
	ashu tripathi <er.ashutripathi@...il.com>,
	nishant gulhane <nishant.s.gulhane@...il.com>,
	amarmore2006 <amarmore2006@...il.com>,
	Shreyas Mahure <shreyas.mahure@...il.com>,
	mahesh mohan <mahesh6490@...il.com>
Subject: Re: [RFC 0/2] kvm: Transcendent Memory (tmem) on KVM

On 03/08/2012 06:29 PM, Akshay Karle wrote:
> Hi,
>
> We are undergraduate engineering students of Maharashtra Academy of
> Engineering, Pune, India and we are working on a project entitled
> 'Transcendent Memory on KVM' as a part of our academics.
> The project members are:
> 1. Ashutosh Tripathi
> 2. Shreyas Mahure
> 3. Nishant Gulhane
> 4. Akshay Karle
>
> ---
> Project Description:
> What is Transcendent Memory(tmem in short)?
> Transcendent Memory is a memory optimization technique for the
> virtualized environment. It collects the underutilized memory of the
> guests and the unassigned(fallow) memory of the host and places it into
> a central tmem pool. Indirect access to this pool is then provided to the guests.
> For further information on tmem, please refer the article on lwn by Dr.
> Dan Magenheimer:
> http://lwn.net/Articles/454795/
>
> Since kvm is one of the most popular hypervisors available,
> we decided to implement this technique for kvm.
>
> Any comments/feedback would be appreciated and will help us a lot with our work.
>

One of the potential problems with tmem is reduction in performance when
the cache hit rate is low, for example when streaming.

Can you test this by creating a large file, for example with

  dd < /dev/urandom > file bs=1M count=100000

and then measuring the time to stream it, using

  time dd < file > /dev/null

with and without the patch?

Should be done on a cleancache enabled guest filesystem backed by a
virtio disk with cache=none.

It would be interesting to compare kvm_stat during the streaming, with
and without the patch.

-- 
error compiling committee.c: too many arguments to function

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