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Date: Mon, 31 Jan 2022 17:32:09 +1100 From: Alistair Popple <apopple@...dia.com> To: <akpm@...ux-foundation.org>, <Felix.Kuehling@....com>, <linux-mm@...ck.org>, <rcampbell@...dia.com>, <linux-ext4@...r.kernel.org>, <linux-xfs@...r.kernel.org>, Alex Sierra <alex.sierra@....com> CC: <amd-gfx@...ts.freedesktop.org>, <dri-devel@...ts.freedesktop.org>, <hch@....de>, <jgg@...dia.com>, <jglisse@...hat.com>, <willy@...radead.org> Subject: Re: [PATCH v5 02/10] mm: add device coherent vma selection for memory migration On Saturday, 29 January 2022 7:08:17 AM AEDT Alex Sierra wrote: [...] > struct migrate_vma { > diff --git a/mm/migrate.c b/mm/migrate.c > index cd137aedcfe5..d3cc3589e1e8 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -2264,7 +2264,8 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, > if (is_writable_device_private_entry(entry)) > mpfn |= MIGRATE_PFN_WRITE; > } else { > - if (!(migrate->flags & MIGRATE_VMA_SELECT_SYSTEM)) > + if (!(migrate->flags & MIGRATE_VMA_SELECT_SYSTEM) && > + !(migrate->flags & MIGRATE_VMA_SELECT_DEVICE_COHERENT)) > goto next; > pfn = pte_pfn(pte); > if (is_zero_pfn(pfn)) { Sorry, but I still don't think this is quite right. When specifying MIGRATE_VMA_SELECT_DEVICE_COHERENT we are looking for pages to migrate from the device back to system memory. But as currently written I think this can also select the zero pfn when MIGRATE_VMA_SELECT_DEVICE_COHERENT is specified. As far as I know that can never point to device memory so migration of a zero pfn should be also be skipped in that case. We should only migrate the zero pfn if MIGRATE_VMA_SELECT_SYSTEM is specified. > @@ -2273,6 +2274,13 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, > goto next; > } > page = vm_normal_page(migrate->vma, addr, pte); > + if (page && !is_zone_device_page(page) && > + !(migrate->flags & MIGRATE_VMA_SELECT_SYSTEM)) > + goto next; > + if (page && is_device_coherent_page(page) && > + (!(migrate->flags & MIGRATE_VMA_SELECT_DEVICE_COHERENT) || > + page->pgmap->owner != migrate->pgmap_owner)) > + goto next; > mpfn = migrate_pfn(pfn) | MIGRATE_PFN_MIGRATE; > mpfn |= pte_write(pte) ? MIGRATE_PFN_WRITE : 0; > } >
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