linux-kernel - Re: [PATCH] Revert "mm, hugetlb: remove hugepages_treat_as

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Message-ID: <aOa_A_i1HUt1wzCj@gourry-fedora-PF4VCD3F>
Date: Wed, 8 Oct 2025 15:44:03 -0400
From: Gregory Price <gourry@...rry.net>
To: David Hildenbrand <david@...hat.com>
Cc: linux-mm@...ck.org, corbet@....net, muchun.song@...ux.dev,
	osalvador@...e.de, akpm@...ux-foundation.org, hannes@...xchg.org,
	laoar.shao@...il.com, brauner@...nel.org, mclapinski@...gle.com,
	joel.granados@...nel.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, Mel Gorman <mgorman@...e.de>,
	Michal Hocko <mhocko@...e.com>,
	Alexandru Moise <00moses.alexander00@...il.com>,
	David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH] Revert "mm, hugetlb: remove hugepages_treat_as_movable
 sysctl"

On Wed, Oct 08, 2025 at 09:01:09PM +0200, David Hildenbrand wrote:
> > 
> > fwiw this works cleanly.  Just dropping this here, but should continue
> > the zone conversation.  I need to check, but does this actually allow
> > pinnable allocations?  I thought pinning kicked off migration.
> 
> Yes, it should because longterm pinning -> unmovable.
> 

You know i just realized, my test here only works before I allocated 1GB
pages on both node0 and node1.  If I only allocate 1gb hugetlb on node1,
then the migrate pages call fails - because there are no 1gb pages
available there.

I imagine this would cause hot-unplug/offline to fail since it uses the
same migration mechanisms.

Worse I would imagine this would fail for 2MB.

Seems like the 1GB limitation is arbitrary if 2MB causes the same issue.

~Gregory