linux-kernel - Re: [PATCH v6 1/5] mm/zone_device: Reinitialize large zone device private folios

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Message-ID: <20260120135340.GA1134360@nvidia.com>
Date: Tue, 20 Jan 2026 09:53:40 -0400
From: Jason Gunthorpe <jgg@...dia.com>
To: Zi Yan <ziy@...dia.com>
Cc: Balbir Singh <balbirs@...dia.com>, Matthew Wilcox <willy@...radead.org>,
	Alistair Popple <apopple@...dia.com>,
	Matthew Brost <matthew.brost@...el.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Francois Dugast <francois.dugast@...el.com>,
	intel-xe@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
	adhavan Srinivasan <maddy@...ux.ibm.com>,
	Nicholas Piggin <npiggin@...il.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	"Christophe Leroy (CS GROUP)" <chleroy@...nel.org>,
	Felix Kuehling <Felix.Kuehling@....com>,
	Alex Deucher <alexander.deucher@....com>,
	Christian König <christian.koenig@....com>,
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	Lyude Paul <lyude@...hat.com>, Danilo Krummrich <dakr@...nel.org>,
	David Hildenbrand <david@...nel.org>,
	Oscar Salvador <osalvador@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Leon Romanovsky <leon@...nel.org>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	"Liam R . Howlett" <Liam.Howlett@...cle.com>,
	Mike Rapoport <rppt@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Michal Hocko <mhocko@...e.com>, linuxppc-dev@...ts.ozlabs.org,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	amd-gfx@...ts.freedesktop.org, nouveau@...ts.freedesktop.org,
	linux-mm@...ck.org, linux-cxl@...r.kernel.org
Subject: Re: [PATCH v6 1/5] mm/zone_device: Reinitialize large zone device
 private folios

On Mon, Jan 19, 2026 at 09:50:16PM -0500, Zi Yan wrote:
> >> I suppose we want some prep_single_page(page) and some reorg to share
> >> code with the other prep function.
> 
> This is just an unnecessary need due to lack of knowledge of/do not want
> to investigate core MM page and folio initialization code.

It will be better to keep this related code together, not spread all
around.

> >> I don't think so. It should do the above job efficiently and iterate
> >> over the page list exactly once.
> 
> folio initialization should not iterate over any page list, since folio is
> supposed to be treated as a whole instead of individual pages.

The tail pages need to have the right data in them or compound_head
won't work.

> folio->mapping = NULL;
> folio->memcg_data = 0;
> folio->flags.f &= ~PAGE_FLAGS_CHECK_AT_PREP;
> 
> should be enough.

This seems believable to me for setting up an order 0 page.

> if (order)
> 	folio_set_large_rmappable(folio);

That one is in zone_device_folio_init()

And maybe the naming has got really confused if we have both functions
now :\

Jason