On Tue, Apr 20, 2021 at 11:45:55AM +0200, Michal Hocko wrote:
> On Fri 16-04-21 13:24:06, Oscar Salvador wrote:
> > From: David Hildenbrand <david@xxxxxxxxxx>
> >
> > Let's have a single place (inspired by adjust_managed_page_count()) where
> > we adjust present pages.
> > In contrast to adjust_managed_page_count(), only memory onlining/offlining
> > is allowed to modify the number of present pages.
> >
> > Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
> > Signed-off-by: Oscar Salvador <osalvador@xxxxxxx>
> > Reviewed-by: Oscar Salvador <osalvador@xxxxxxx>
>
> Not sure self review counts ;)
Uhm, the original author is David, I just added my signed-off-by as a deliverer.
I thought that in that case was ok to stick my Reviewed-by.
Or maybe my signed-off-by carries that implicitly.
> Acked-by: Michal Hocko <mhocko@xxxxxxxx>
>
> Btw. I strongly suspect the resize lock is quite pointless here.
> Something for a follow up patch.
What makes you think that?
I have been thinking about this, let us ignore this patch for a moment.
If I poked the code correctly, node_size_lock is taken in:
remove_pfn_range_from_zone()
move_pfn_range_to_zone()
both of them handling {zone,node}->spanned_pages
Then we take it in {offline,online}_pages() for {zone,node}->present_pages.
The other places where we take it are __init functions, so not of interest.
Given that {offline,online}_pages() is serialized by the memory_hotplug lock,
I would say that {node,zone}->{spanned,present}_pages is, at any time, stable?
So, no need for the lock even without considering this patch?
Now, getting back to this patch.
adjust_present_page_count() will be called from memory_block_online(), which
is not holding the memory_hotplug lock yet.
But, we only fiddle with present pages out of {online,offline}_pages() if
we have vmemmap pages, and since that operates on the same memory block,
its lock should serialize that.
I think I went down a rabbit hole, I am slightly confused now.
--
Oscar Salvador
SUSE L3
