Date: Fri, 20 May 2011 01:25:20 +0200
From: Daniel Kiper <dkiper@net-space.pl>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Daniel Kiper <dkiper@net-space.pl>, David Rientjes <rientjes@google.com>,
        ian.campbell@citrix.com, haicheng.li@linux.intel.com,
        fengguang.wu@intel.com, jeremy@goop.org, konrad.wilk@oracle.com,
        dan.magenheimer@oracle.com, v.tolstov@selfip.ru, pasik@iki.fi,
        dave@linux.vnet.ibm.com, wdauchy@gmail.com,
        xen-devel@lists.xensource.com, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [PATCH V3 2/2] mm: Extend memory hotplug API to allow memory hotplug in virtual machines
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References: <20110517213858.GC30232@router-fw-old.local.net-space.pl> <alpine.DEB.2.00.1105182026390.20651@chino.kir.corp.google.com> <20110519204509.GD27202@router-fw-old.local.net-space.pl> <20110519160143.02163f36.akpm@linux-foundation.org>
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On Thu, May 19, 2011 at 04:01:43PM -0700, Andrew Morton wrote:
> On Thu, 19 May 2011 22:45:09 +0200
> Daniel Kiper <dkiper@net-space.pl> wrote:
>
> > On Wed, May 18, 2011 at 08:36:02PM -0700, David Rientjes wrote:
> > > On Tue, 17 May 2011, Daniel Kiper wrote:
> > >
> > > > This patch contains online_page_callback and apropriate functions for
> > > > setting/restoring online page callbacks. It allows to do some machine
> > > > specific tasks during online page stage which is required to implement
> > > > memory hotplug in virtual machines. Additionally, __online_page_set_limits(),
> > > > __online_page_increment_counters() and __online_page_free() function
> > > > was added to ease generic hotplug operation.
> > >
> > > There are several issues with this.
> > >
> > > First, this is completely racy and only allows one global callback to be
> > > in use at a time without looping, which is probably why you had to pass an
> >
> > One callback is allowed by design. Currently I do not see
> > any real usage for more than one callback.
>
> I'd suggest that you try using the notifier.h tools here and remove the
> restriction.  Sure, we may never use the capability but I expect the
> code will look nice and simple and once it's done, it's done.

Hmmm... I am a bit confused. Here https://lkml.org/lkml/2011/3/28/510 you
was against (ab)using notifiers. Here https://lkml.org/lkml/2011/3/29/313
you proposed currently implemented solution. Maybe I missed something...
What should I do now ??? I agree that the code should look nice and simple
and once it's done, it's done.

Daniel
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