Re: Hotplug memory remove

[Mark Gross <mgross@linux.intel.com>]

On Sat, Oct 06, 2007 at 09:41:15AM +0900, KAMEZAWA Hiroyuki wrote:
> On Fri, 5 Oct 2007 10:21:28 -0700
> Mark Gross <mgross@linux.intel.com> wrote:
> 
> > > I'm not sure about this...does this memory is in ZONE_MOVABLE ?
> > > If not ZONE_MOVABLE, offlining can be fail because of not-removable
> > > kernel memory. 
> > 
> > How could I mark a nid's worth of memory as ZONE_MOVABLE?  I've been
> > reading through this code and it appears to somewhat arbitrarily choose
> > some portion of the memory to be ZONE_MOVABLE per pxm and some kernel
> > parameters.  But I'm having a hard time finding the proper place to set
> > up the nodes.
> > 
> It's not available now.

Thats a usability challenge.  What use scenarios do you have for memory
unplug then?  I'd like to mimic your stuff if I can.

> 
> One idea is to ignore memory of some PXMs specified by kerenel boot param.
> Later, you can hot-add specified PXM memory as MOVABLE.
> Then, boot sequence will be
> --
>    bootstrap , ignore some memory here.
>    init memory, driver, etc
>    hot-add ignored memory
>    online hot-added memory by user scripts. (from rc script ?)
> --y
> For doing this, we need
>  - a switch to hot-add memory as MOVABLE (will be easy patch)
>  - a code for ignoring memory at boot but remember them for later hotadd
>    (maybe needs arch specific codes)
>  - a code for hot add memory before rc script (initcall is suitable ?) 
> 
> Needs some amount of arch-specific codes, but maybe simple.
> Why I recommend above is it will be complex to avoid some PXM's memory
> to be used as bootmem or for some other purpose(slab, hash, etc...).

I have the boot memory allocations or off-lineable-memory taken care of.
I can see how the above would work, but I worry that it feels a bit
hackish.   

BTW Is this how memory hot remove is expected to be used?

> 
> If your firmware (efi?) doesn't show memory for hot removal at boot time,
> this idea will be simpler..

how so?  

thanks,

--mgross

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