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

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Message-ID: <20210601103334.GA5927@linux>
Date:   Tue, 1 Jun 2021 12:33:43 +0200
From:   Oscar Salvador <osalvador@...e.de>
To:     Michal Hocko <mhocko@...e.com>
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, Jun 01, 2021 at 11:47:13AM +0200, Michal Hocko wrote:
> 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.

I am not sure about that. True is that deferred_init_memmap() gets executed
on numa-thread so it's not a problem for itself, but we also have deferred_grow_zone().
It might be that while deferred_init_memmap() is running, we also have calls to
deferred_grow_zone() for the same node and that would cause some trouble wrt.
first_deferred_pfn. I need to double check it, but IIRC, that is the case.


-- 
Oscar Salvador
SUSE L3