linux-kernel - Re: [PATCH 3/5] mm: Rename __thp_get_unmapped_area to mm_get_unmapped_area

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Message-ID: <20250616122630.GT1174925@nvidia.com>
Date: Mon, 16 Jun 2025 09:26:30 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: "Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Peter Xu <peterx@...hat.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, kvm@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alex Williamson <alex.williamson@...hat.com>,
	Zi Yan <ziy@...dia.com>, Alex Mastro <amastro@...com>,
	David Hildenbrand <david@...hat.com>,
	Nico Pache <npache@...hat.com>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	Ryan Roberts <ryan.roberts@....com>, Dev Jain <dev.jain@....com>,
	Barry Song <baohua@...nel.org>
Subject: Re: [PATCH 3/5] mm: Rename __thp_get_unmapped_area to
 mm_get_unmapped_area_aligned

On Mon, Jun 16, 2025 at 01:20:55PM +0100, Lorenzo Stoakes wrote:
> On Mon, Jun 16, 2025 at 09:14:28AM -0300, Jason Gunthorpe wrote:
> > Also, probably 'aligned' is not the right name. This new function
> > should be called by VMA owners that know they have pgoff aligned high
> > order folios/pfns inside their mapping. The 'align' argument is the
> > max order of their pgoff aligned folio/pfns.
> >
> > The purpose of the function is to adjust the resulting area to
> > optimize for the high order folios that are present while following
> > the uAPI rules for mmap.
> >
> > Maybe call it something like _order and document it like the above?
> 
> Right, if it were made clear this is explicitly related to higher order
> folios that would go a long way to making the generalisation more
> acceptable.
> 
> But we definitely need to have it not filter errors if it's generic.
> 
> >
> >
> > > I also am not okay to export it for no reason.
> >
> > The next patches are the reason.
> 
> Regardless exporting it like this raises the bar for quality here.

Yes, it is also possible we have the wrong op, I know
get_unmapped_area() pre-exists, but if we are really cleaning this
stuff then something like get_max_pte_order() is probably a saner op.

It would return the size of the biggest pgoff aligned folio/pfn within
the file. Then the core code would do the special logic without
exporting this function.

Jason