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Date: Thu, 12 May 2022 12:58:00 +1000 From: Alistair Popple <apopple@...dia.com> To: Alex Sierra <alex.sierra@....com> Cc: jgg@...dia.com, david@...hat.com, Felix.Kuehling@....com, linux-mm@...ck.org, rcampbell@...dia.com, linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org, amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org, hch@....de, jglisse@...hat.com, willy@...radead.org, akpm@...ux-foundation.org Subject: Re: [PATCH v1 01/15] mm: add zone device coherent type memory support Alex Sierra <alex.sierra@....com> writes: [...] > diff --git a/mm/rmap.c b/mm/rmap.c > index fedb82371efe..d57102cd4b43 100644 > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -1995,7 +1995,8 @@ void try_to_migrate(struct folio *folio, enum ttu_flags flags) > TTU_SYNC))) > return; > > - if (folio_is_zone_device(folio) && !folio_is_device_private(folio)) > + if (folio_is_zone_device(folio) && > + (!folio_is_device_private(folio) && !folio_is_device_coherent(folio))) > return; > > /* I vaguely recall commenting on this previously, or at least intending to. In try_to_migrate_one() we have this: if (folio_is_zone_device(folio)) { unsigned long pfn = folio_pfn(folio); swp_entry_t entry; pte_t swp_pte; /* * Store the pfn of the page in a special migration * pte. do_swap_page() will wait until the migration * pte is removed and then restart fault handling. */ entry = pte_to_swp_entry(pteval); if (is_writable_device_private_entry(entry)) entry = make_writable_migration_entry(pfn); else entry = make_readable_migration_entry(pfn); swp_pte = swp_entry_to_pte(entry); The check in try_to_migrate() guarantees that if folio_is_zone_device() is true this must be a DEVICE_PRIVATE page and it treats it as such by assuming there is a special device private swap entry there. Relying on that assumption seems bad, and I have no idea why I didn't just use is_device_private_page() originally but I think the fix is just to change this to: if (folio_is_device_private(folio)) And let DEVICE_COHERENT pages fall through to normal page processing. - Alistair
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