Re: [HMM 01/16] mm/memory/hotplug: add memory type parameter to arch_add/remove_memory

From: Jerome Glisse <jglisse@redhat.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, John Hubbard <jhubbard@nvidia.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
	David Nellans <dnellans@nvidia.com>,
	Russell King <linux@armlinux.org.uk>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Martin Schwidefsky <schwidefsky@de.ibm.com>,
	Heiko Carstens <heiko.carstens@de.ibm.com>,
	Yoshinori Sato <ysato@users.sourceforge.jp>,
	Rich Felker <dalias@libc.org>,
	Chris Metcalf <cmetcalf@mellanox.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [HMM 01/16] mm/memory/hotplug: add memory type parameter to arch_add/remove_memory
Date: Fri, 7 Apr 2017 10:32:49 -0400	[thread overview]
Message-ID: <20170407143246.GA15098@redhat.com> (raw)
In-Reply-To: <20170407121349.GB16392@dhcp22.suse.cz>

On Fri, Apr 07, 2017 at 02:13:49PM +0200, Michal Hocko wrote:
> On Wed 05-04-17 16:40:11, Jérôme Glisse wrote:
> > When hotpluging memory we want more information on the type of memory.
> > This is to extend ZONE_DEVICE to support new type of memory other than
> > the persistent memory. Existing user of ZONE_DEVICE (persistent memory)
> > will be left un-modified.
> 
> My current hotplug rework [1] is touching this path as well. It is not
> really clear from the chage why you are changing this and what are the
> further expectations of MEMORY_DEVICE_PERSISTENT. Infact I have replaced
> for_device with want__memblock [2]. I plan to repost shortly but I would
> like to understand your modifications more to reduce potential conflicts
> in the code. Why do you need to distinguish different types of memory
> anyway.
> 
> [1] http://lkml.kernel.org/r/20170330115454.32154-1-mhocko@kernel.org
> [2] the current patchset is in git://git.kernel.org/pub/scm/linux/kernel/git/mhocko/mm.git
>     branch attempts/rewrite-mem_hotplug-WIP

This is needed for UNADDRESSABLE memory type introduced in patch 3 and
the arch specific bits are in patch 4. Basicly for UNADDRESSABLE memory
i do not want the arch code to create a linear mapping for the range
being hotpluged. Adding memory_type in this patch allow to distinguish
between different type of ZONE_DEVICE.

After your patchset, we do not need the for_device but i still need to
know if it is UNADDRESSABLE. You can check my branch on top of your
previous patchset (again patch 1, 3 and 4):

https://cgit.freedesktop.org/~glisse/linux/commit/?h=hmm-v20

1:
https://cgit.freedesktop.org/~glisse/linux/commit/?h=hmm-v20&id=a85a895615e4812d3c68869cfeef92a4924b4946
3:
https://cgit.freedesktop.org/~glisse/linux/commit/?h=hmm-v20&id=539b6d12429a7166f3690944d6bf164930a59def
4:
https://cgit.freedesktop.org/~glisse/linux/commit/?h=hmm-v20&id=d5338b868e801acabb96c7166c1e802d730511e3

I will check your new branch and see what want_memblock is for.

Cheers,
Jérôme