On 30.06.22 13:44, Alistair Popple wrote: > > David Hildenbrand <david@xxxxxxxxxx> writes: > >> On 29.06.22 05:54, Alex Sierra wrote: >>> This case is used to migrate pages from device memory, back to system >>> memory. Device coherent type memory is cache coherent from device and CPU >>> point of view. >>> >>> Signed-off-by: Alex Sierra <alex.sierra@xxxxxxx> >>> Acked-by: Felix Kuehling <Felix.Kuehling@xxxxxxx> >>> Reviewed-by: Alistair Poppple <apopple@xxxxxxxxxx> >>> Signed-off-by: Christoph Hellwig <hch@xxxxxx> >> >> >> I'm not too familiar with this code, please excuse my naive questions: >> >>> @@ -148,15 +148,21 @@ 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)) >>> - goto next; >> >> Why not exclude MIGRATE_VMA_SELECT_DEVICE_PRIVATE here? IIRC that would >> have happened before this change. > > I might be missing something as I don't quite follow - this path is for > normal system pages so we only want to skip selecting them if > MIGRATE_VMA_SELECT_SYSTEM or MIGRATE_VMA_SELECT_DEVICE_COHERENT aren't > set. > > Note that MIGRATE_VMA_SELECT_DEVICE_PRIVATE doesn't apply here because > we already know it's not a device private page by virtue of > pte_present(pte) == True. Ah, stupid me, pte_present(pte) is the key. > >>> pfn = pte_pfn(pte); >>> - if (is_zero_pfn(pfn)) { >>> + if (is_zero_pfn(pfn) && >>> + (migrate->flags & MIGRATE_VMA_SELECT_SYSTEM)) { >>> mpfn = MIGRATE_PFN_MIGRATE; >>> migrate->cpages++; >>> goto next; >>> } >>> page = vm_normal_page(migrate->vma, addr, pte); >>> + if (page && !is_zone_device_page(page) && >> >> I'm wondering if that check logically belongs into patch #2. > > I don't think so as it would break functionality until the below > conditionals are added - we explicitly don't want to skip > is_zone_device_page(page) == False here because that is the pages we are > trying to select. > > You could add in this: > >>> + !(migrate->flags & MIGRATE_VMA_SELECT_SYSTEM)) > > But then in patch 2 we know this can never be true because we've already > checked for !MIGRATE_VMA_SELECT_SYSTEM there. Ah, okay, thanks Reviewed-by: David Hildenbrand <david@xxxxxxxxxx> -- Thanks, David / dhildenb