Messages in this thread | | | Date | Wed, 21 Apr 2021 10:00:36 +0200 | From | Oscar Salvador <> | Subject | Re: [PATCH v9 3/8] mm,memory_hotplug: Factor out adjusting present pages into adjust_present_page_count() |
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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@redhat.com> > > > > 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@redhat.com> > > Signed-off-by: Oscar Salvador <osalvador@suse.de> > > Reviewed-by: Oscar Salvador <osalvador@suse.de> > > 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@suse.com> > > 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
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