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

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Message-ID: <aOZ8PPWMchRN_t5-@tiehlicka>
Date: Wed, 8 Oct 2025 16:59:08 +0200
From: Michal Hocko <mhocko@...e.com>
To: David Hildenbrand <david@...hat.com>
Cc: Gregory Price <gourry@...rry.net>, 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>,
	Alexandru Moise <00moses.alexander00@...il.com>,
	Mike Kravetz <mike.kravetz@...cle.com>,
	David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH] Revert "mm, hugetlb: remove hugepages_treat_as_movable
 sysctl"

On Wed 08-10-25 10:58:23, David Hildenbrand wrote:
> On 07.10.25 23:44, Gregory Price wrote:
[...]
> > @@ -926,7 +927,8 @@ static inline gfp_t htlb_alloc_mask(struct hstate *h)
> >   {
> >   	gfp_t gfp = __GFP_COMP | __GFP_NOWARN;
> > -	gfp |= hugepage_movable_supported(h) ? GFP_HIGHUSER_MOVABLE : GFP_HIGHUSER;
> > +	gfp |= (hugepage_movable_supported(h) || hugepages_treat_as_movable) ?
> > +	       GFP_HIGHUSER_MOVABLE : GFP_HIGHUSER;
> 
> I mean, this is as ugly as it gets.
> 
> Can't we just let that old approach RIP where it belongs? :)
> 
> If something unmovable, it does not belong on ZONE_MOVABLE, as simple as that.

yes, I do agree. This is just muddying the semantic of the zone.

Maybe what we really want is to have a configurable zone rather than a
very specific consumer of it instead. What do I mean by that? We clearly
have physically (DMA, DMA32) and usability (NORMAL, MOVABLE) constrained
zones. So rather than having a MOVABLE zone we can have a single zone
$FOO_NAME zone with configurable attributes - like allocation
constrains (kernel, user, movable, etc). Now that we can overlap zones
this should allow for quite a lot flexibility. Implementation wise this
would require some tricks as we have 2 zone types for potentially 3
different major usecases (kernel allocations, userspace reserved ranges
without movability and movable allocations). I haven't thought this
through completely and mostly throwing this as an idea (maybe won't
work). Does that make sense?
-- 
Michal Hocko
SUSE Labs