Re: [PATCH] mm: fix movable_node kernel command-line

[Michal Hocko <mhocko@kernel.org>]

On Mon 23-10-17 10:35:44, Sharath Kumar Bhat wrote:
> On Mon, Oct 23, 2017 at 07:20:08PM +0200, Michal Hocko wrote:
> > On Mon 23-10-17 10:14:35, Sharath Kumar Bhat wrote:
> > [...]
> > > This lets admin to configure the kernel to have movable memory > size of
> > > hotpluggable memories and at the same time hotpluggable nodes have only
> > > movable memory.
> > 
> > Put aside that I believe that having too much of movable memory is
> > dangerous and people are not very prepared for that fact, what is the
> > specific usecase. Allowing users something is nice but as I've said the
> > interface is ugly already and putting more on top is not very desirable.
> > 
> > > This is useful because it lets user to have more movable
> > > memory in the system that can be offlined/onlined. When the same hardware
> > > is shared between two OS's then this helps to dynamically provision the
> > > physical memory between them by offlining/onlining as and when the
> > > application/user need changes.
> > 
> > just use hotplugable memory for that purpose. The latest memory hotplug
> > code allows you to online memory into a kernel or movable zone as per
> > admin policy without the previously hardcoded zone ordering. So I really
> > fail to see why to mock with the command line parameter at all.
> 
> Yes, but it won't let us offline the memory blocks if they are already
> in use by kernel allocations. This is more likely over a long period of
> uptime. The command-line ensures that the memory blocks are movable all
> the time as reserved by the admin from the boot.

I am really confused about your usecase then. Why do you want to make
non-hotplugable memory to be movable then?

-- 
Michal Hocko
SUSE Labs

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