Re: [PATCH v1 1/2] mm/page_alloc.c: Don't set pages PageReserved() when offlining

[Michal Hocko]

On Mon 21-10-19 17:39:36, David Hildenbrand wrote:
> On 21.10.19 16:43, Michal Hocko wrote:
[...]
> > We still set PageReserved before onlining pages and that one should be
> > good to go as well (memmap_init_zone).
> > Thanks!
> 
> memmap_init_zone() is called when onlining memory. There, set all pages to
> reserved right now (on context == MEMMAP_HOTPLUG). We clear PG_reserved when
> onlining a page to the buddy (e.g., generic_online_page). If we would online
> a memory block with holes, we would want to keep all such pages
> (!pfn_valid()) set to reserved. Also, there might be other side effects.

Isn't it sufficient to have those pages in a poisoned state? They are
not onlined so their state is basically undefined anyway. I do not see
how PageReserved makes this any better.

Also is the hole inside a hotplugable memory something we really have to
care about. Has anybody actually seen a platform to require that?
-- 
Michal Hocko
SUSE Labs