Date: Wed, 07 Apr 2004 15:33:38 -0700
From: "Martin J. Bligh" <mbligh@aracnet.com>
To: Mike Kravetz <kravetz@us.ibm.com>
cc: IWAMOTO Toshihiro <iwamoto@valinux.co.jp>, linux-kernel@vger.kernel.org,
       lhms-devel@lists.sourceforge.net
Subject: Re: [Lhms-devel] Re: [patch 0/3] memory hotplug prototype
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References: <20040406105353.9BDE8705DE@sv1.valinux.co.jp> <29700000.1081361575@flay> <20040407185953.GC4292@w-mikek2.beaverton.ibm.com>
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--On Wednesday, April 07, 2004 11:59:53 -0700 Mike Kravetz <kravetz@us.ibm.com> wrote:

> On Wed, Apr 07, 2004 at 11:12:55AM -0700, Martin J. Bligh wrote:
>> > This is an updated version of memory hotplug prototype patch, which I
>> > have posted here several times.
>> 
>> I really, really suggest you take a look at Dave McCracken's work, which
>> he posted as "Basic nonlinear for x86" recently. It's going to be much
>> much easier to use this abstraction than creating 1000s of zones ...
>> 
> 
> I agree.  However, one could argue that taking a zone offline is 'easier'
> than taking a 'section' offline: at least right now.  Note that I said
> easier NOT better.  Currently a section represents a subset of one or more
> zones.  Ideally, these sections represent units that can be added or
> removed.  IIRC these sections only define a range of physical memory.
> To determine if it is possible to take a section offline, one needs to
> dig into the zone(s) that the section may be associated with.  We'll
> have to do things like:
> - Stop allocations of pages associated with the section.
> - Grab all 'free pages' associated with the section.
> - Try to reclaim/free all pages associated with the section.
>   - Work on this until all pages in the section are not in use (or free).
>   - OR give up if we know we will not succeed.
> 
> My claim of zones being easier to work with today is due to the
> fact that zones contain much of the data/infrastructure to make
> these types of operations easy.  For example, in IWAMOTO's code a
> node/zone can be take offline when 'z->present_pages == z->free_pages'.

I really think the level of difference in difficultly here is trivial.
The hard bit is freeing the pages, not measuring them. I would suspect
altering the swap path to just not "free" the pages, but put them into
a pool for hotplug is fairly easy.

M.

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