linux-kernel - Re: [PATCH] mm,memory_hotplug: Drop unneeded locking

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Message-ID: <YLYCIZ5XNXGoE95p@dhcp22.suse.cz>
Date:   Tue, 1 Jun 2021 11:47:13 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Oscar Salvador <osalvador@...e.de>
Cc:     David Hildenbrand <david@...hat.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Pavel Tatashin <pasha.tatashin@...een.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm,memory_hotplug: Drop unneeded locking

On Tue 01-06-21 10:12:54, Oscar Salvador wrote:
> On Tue, Jun 01, 2021 at 10:02:54AM +0200, David Hildenbrand wrote:
> > If there is no writer anymore, why do we have to protect readers?
> 
> Yeah, you are right. 
> Let me prepare a v2 as this is getting too sloppy.

While you are touching this and want to drill all the way down then it
would be reasonable to drop pgdat resize locks as well.
It is only used in the early boot code and we have one executing thread
context per numa node during the deferred initialization. I haven't
checked all potential side effects the lock might have but it sounds
like there is quite some clean up potential over there.

-- 
Michal Hocko
SUSE Labs