linux-kernel - Re: [PATCH] huge_memory: return -EINVAL in folio split functions when THP is disabled

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Message-ID: <ic5kobuxfm4zi6agfvosjxs325mdgrfpjz52mi3zn27epbuvef@z5dmowge6uyb>
Date: Tue, 2 Sep 2025 15:40:39 +0200
From: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>
To: Kiryl Shutsemau <kirill@...temov.name>
Cc: David Hildenbrand <david@...hat.com>, 
	Ryan Roberts <ryan.roberts@....com>, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, 
	Baolin Wang <baolin.wang@...ux.alibaba.com>, Dev Jain <dev.jain@....com>, Barry Song <baohua@...nel.org>, 
	Andrew Morton <akpm@...ux-foundation.org>, Nico Pache <npache@...hat.com>, Zi Yan <ziy@...dia.com>, 
	"Liam R . Howlett" <Liam.Howlett@...cle.com>, linux-kernel@...r.kernel.org, linux-mm@...ck.org, 
	willy@...radead.org, mcgrof@...nel.org, gost.dev@...sung.com, 
	Pankaj Raghav <p.raghav@...sung.com>
Subject: Re: [PATCH] huge_memory: return -EINVAL in folio split functions
 when THP is disabled

> > 
> > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> > index 48c4f91c5b13..4ddf9e87db91 100644
> > --- a/include/linux/huge_mm.h
> > +++ b/include/linux/huge_mm.h
> > @@ -588,21 +588,29 @@ static inline int
> >  split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
> >                 unsigned int new_order)
> >  {
> > +       struct folio *folio = page_folio(page);
> > +
> > +       VM_WARN_ON_ONCE_FOLIO(!folio_test_large(folio), folio);
> 
> No. Make it unconditional. The point is we don't expect to see any
> splitable folios, so no reason to get here at all.
> 

Got it.

Just one question though, in a future world where we remove the
dependency between large folios and THP, then we can revert back
this change to do a conditional WARN_ON?

--
Pankaj