Re: [PATCH v2 3/3] mm: enable CONFIG_MOVABLE_NODE on powerpc

From: Reza Arbab
Date: Wed Sep 21 2016 - 10:10:34 EST

On Wed, Sep 21, 2016 at 12:39:51PM +0530, Aneesh Kumar K.V wrote:
What I was checking was how will one mark a node movable in ppc64 ? I
don't see ppc64 code doing the equivalent of memblock_mark_hotplug().

Post boot, the marking mechanism is not necessary. You can create a movable node by putting all of the node's memory into ZONE_MOVABLE during the hotplug.

So when you say "Onlining memory into ZONE_MOVABLE requires
CONFIG_MOVABLE_NODE" where is that restriction ?. IIUC,
should_add_memory_movable() will only return ZONE_MOVABLE only if it is
non empty and MOVABLE_NODE will create a ZONE_MOVABLE zone by default
only if it finds a memblock marked hotpluggable. So wondering if we
are not calling memblock_mark_hotplug() how is it working. Or am I
missing something ?

You are looking at the addition step of hotplug. You're correct there, the memory is added to the default zone, not ZONE_MOVABLE. The transition to ZONE_MOVABLE takes place during the onlining step. In online_pages():

zone = move_pfn_range(zone_shift, pfn, pfn + nr_pages);

The reason we need CONFIG_MOVABLE_NODE is right before that:

if ((zone_idx(zone) > ZONE_NORMAL ||
online_type == MMOP_ONLINE_MOVABLE) &&
return -EINVAL;

where can_online_high_movable() is defined like this:

* When CONFIG_MOVABLE_NODE, we permit onlining of a node which doesn't have
* normal memory.
static bool can_online_high_movable(struct zone *zone)
return true;
/* ensure every online node has NORMAL memory */
static bool can_online_high_movable(struct zone *zone)
return node_state(zone_to_nid(zone), N_NORMAL_MEMORY);

To be more clear, I can change the commit log to say "Onlining all of a node's memory into ZONE_MOVABLE requires CONFIG_MOVABLE_NODE".

Reza Arbab