linux-kernel - Re: [PATCH] rdma: don't make pages writeable if not requiested

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Message-ID: <20130321174237.GA4060@redhat.com>
Date:	Thu, 21 Mar 2013 19:42:37 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:	Roland Dreier <roland@...nel.org>,
	"Michael R. Hines" <mrhines@...ux.vnet.ibm.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: [PATCH] rdma: don't make pages writeable if not requiested

On Thu, Mar 21, 2013 at 11:21:50AM -0600, Jason Gunthorpe wrote:
> On Thu, Mar 21, 2013 at 07:15:25PM +0200, Michael S. Tsirkin wrote:
> 
> > No because application does this:
> > init page
> > 
> > ...
> > 
> > after a lot of time
> > 
> > ..
> > 
> > register
> > send
> > unregister
> > 
> > so it can not be read only.
> 
> mprotect(READONLY)
> register
> send
> unregister
> mprotect(WRITABLE)
> 
> ?
> With something like GIFT the app already has to give up writing to the
> pages while they are moving, so changing the protection seems in line
> with that?
> 
> Jason

It doesn't actually, and our app would sometimes write to these pages.
It simply does not care which version does the remote get in this case
since we track writes and resend later.

Also this is per-page, MRs have byte granularity so easier to use.

-- 
MST
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