"Sierra Guiza, Alejandro (Alex)" Alex.Sierra@amd.com writes:
@apopple@nvidia.com Could you please check this patch? It's somehow related to migrate_device_page() for long term device coherent pages.
Regards, Alex Sierra
-----Original Message----- From: amd-gfx amd-gfx-bounces@lists.freedesktop.org On Behalf Of Alex Sierra Sent: Thursday, May 5, 2022 4:34 PM To: jgg@nvidia.com Cc: rcampbell@nvidia.com; willy@infradead.org; david@redhat.com; Kuehling, Felix Felix.Kuehling@amd.com; apopple@nvidia.com; amd- gfx@lists.freedesktop.org; linux-xfs@vger.kernel.org; linux-mm@kvack.org; jglisse@redhat.com; dri-devel@lists.freedesktop.org; akpm@linux- foundation.org; linux-ext4@vger.kernel.org; hch@lst.de Subject: [PATCH v1 04/15] mm: add device coherent checker to remove migration pte
During remove_migration_pte(), entries for device coherent type pages that were not created through special migration ptes, ignore _PAGE_RW flag. This path can be found at migrate_device_page(), where valid vma is not required. In this case, migrate_vma_collect_pmd() is not called and special migration ptes are not set.
It's true that we don't call migrate_vma_collect_pmd() for migrate_device_page(), but this doesn't imply migration entries are not created. We still call migrate_vma_unmap() which calls try_to_migrate() to install migration entries.
When we have a vma migrate_vma_collect_pmd() is a fast path for the common case a page is only mapped once. So migrate_vma_collect_pmd() should fairly closely match try_to_migrate_one(). I did experiment locally with removing the fast path to simplify the code, but it does provide a meaningful performance improvement so I abandoned it.
I think you're running into the problem addressed by https://lkml.kernel.org/r/20211018045247.3128058-1-apopple@nvidia.com but for DEVICE_COHERENT pages.
Based on that I think the approach below is wrong. You should update try_to_migrate_one() to deal with DEVICE_COHERENT pages. It would make sense to do that as part of patch 1 in this series.
The problem is that try_to_migrate_one() assumes folio_is_zone_device() implies it is a DEVICE_PRIVATE page due to the check in try_to_migrate().
Signed-off-by: Alex Sierra alex.sierra@amd.com
mm/migrate.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/mm/migrate.c b/mm/migrate.c index 6c31ee1e1c9b..e18ddee56f37 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -206,7 +206,8 @@ static bool remove_migration_pte(struct folio *folio, * Recheck VMA as permissions can change since migration started */ entry = pte_to_swp_entry(*pvmw.pte);
if (is_writable_migration_entry(entry))
if (is_writable_migration_entry(entry) ||is_device_coherent_page(pfn_to_page(pvmw.pfn))) pte = maybe_mkwrite(pte, vma);-- 2.32.0