linux-kernel - Re: [PATCHv2] rdma: add a new IB_ACCESS

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Message-ID: <20130409191218.GD8212@redhat.com>
Date:	Tue, 9 Apr 2013 22:12:18 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Roland Dreier <roland@...nel.org>
Cc:	"Michael R. Hines" <mrhines@...ux.vnet.ibm.com>,
	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	Sean Hefty <sean.hefty@...el.com>,
	Hal Rosenstock <hal.rosenstock@...il.com>,
	Yishai Hadas <yishaih@...lanox.com>,
	Christoph Lameter <cl@...ux.com>,
	"linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>, qemu-devel@...gnu.org
Subject: Re: [PATCHv2] rdma: add a new IB_ACCESS_GIFT flag

On Fri, Apr 05, 2013 at 01:43:49PM -0700, Roland Dreier wrote:
> On Fri, Apr 5, 2013 at 1:17 PM, Michael R. Hines
> <mrhines@...ux.vnet.ibm.com> wrote:
> > I also removed the IBV_*_WRITE flags on the sender-side and activated
> > cgroups with the "memory.memsw.limit_in_bytes" activated and the migration
> > with RDMA also succeeded without any problems (both with *and* without GIFT
> > also worked).
> 
> Not sure I'm interpreting this correctly.  Are you saying that things
> worked without actually setting the GIFT flag?   In which case why are
> we adding this flag?
> 
>  - R.

We are adding the flag to reduce memory when there's lots of COW pages.
There's no guarantee there will be COW pages so I expect things to work
both with and without breaking COW, just using much more memory when we
break COW.

-- 
MST
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