On Fri, Aug 31, 2018 at 12:19:35PM -0400, Jerome Glisse wrote:
On Fri, Aug 31, 2018 at 07:27:24PM +1000, Balbir Singh wrote:
On Thu, Aug 30, 2018 at 10:41:56AM -0400, jglisse@redhat.com wrote:
From: Ralph Campbell rcampbell@nvidia.com
Private ZONE_DEVICE pages use a special pte entry and thus are not present. Properly handle this case in map_pte(), it is already handled in check_pte(), the map_pte() part was lost in some rebase most probably.
Without this patch the slow migration path can not migrate back private ZONE_DEVICE memory to regular memory. This was found after stress testing migration back to system memory. This ultimatly can lead the CPU to an infinite page fault loop on the special swap entry.
Changes since v1: - properly lock pte directory in map_pte()
Signed-off-by: Ralph Campbell rcampbell@nvidia.com Signed-off-by: Jérôme Glisse jglisse@redhat.com Cc: Andrew Morton akpm@linux-foundation.org Cc: Kirill A. Shutemov kirill.shutemov@linux.intel.com Cc: Balbir Singh bsingharora@gmail.com Cc: stable@vger.kernel.org
mm/page_vma_mapped.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c index ae3c2a35d61b..bd67e23dce33 100644 --- a/mm/page_vma_mapped.c +++ b/mm/page_vma_mapped.c @@ -21,7 +21,14 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw) if (!is_swap_pte(*pvmw->pte)) return false; } else {
if (!pte_present(*pvmw->pte))
if (is_swap_pte(*pvmw->pte)) {swp_entry_t entry;/* Handle un-addressable ZONE_DEVICE memory */entry = pte_to_swp_entry(*pvmw->pte);if (!is_device_private_entry(entry))return false;OK, so we skip this pte from unmap since it's already unmapped? This prevents try_to_unmap from unmapping it and it gets restored with MIGRATE_PFN_MIGRATE flag cleared?
Sounds like the right thing, if I understand it correctly
Well not exactly we do not skip it, we replace it with a migration
I think I missed the !is_device_private_entry and missed the ! part, so that seems reasonable
Reviewed-by: Balbir Singh bsingharora@gmail.com