Messages in this thread | | | Subject | Re: [PATCH v9 3/8] mm,memory_hotplug: Factor out adjusting present pages into adjust_present_page_count() | From | David Hildenbrand <> | Date | Wed, 21 Apr 2021 10:06:33 +0200 |
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On 21.04.21 10:00, Oscar Salvador wrote: > 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.
We always hold the device hotplug lock when onlining/offlining memory.
I agree that the lock might be unnecessary (had the same thoughts a while ago), we can look into that in the future.
-- Thanks,
David / dhildenb
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