diff --git a/mm/migrate.c b/mm/migrate.c index 1852d787e6ab..f74422a42192 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -362,7 +362,7 @@ static int expected_page_refs(struct address_space *mapping, struct page *page) * Device private pages have an extra refcount as they are * ZONE_DEVICE pages. */
- expected_count += is_device_private_page(page);
- expected_count += is_device_page(page); if (mapping) expected_count += thp_nr_pages(page) + page_has_private(page);
@@ -2503,7 +2503,7 @@ static bool migrate_vma_check_page(struct page *page) * FIXME proper solution is to rework migration_entry_wait() so * it does not need to take a reference on page. */
Note that I have posted a patch to fix this - see https://lore.kernel.org/all/20211118020754.954425-1-apopple@nvidia.com/ This looks ok for now assuming coherent pages can never be pinned.
However that raises a question - what happens when something calls get_user_pages() on a pfn pointing to a coherent device page? I can't see anything in this series that prevents pinning of coherent device pages, so we can't just assume they aren't pinned.
I agree. I think we need to depend on your patch to go in first.
I'm also wondering if we need to do something to prevent get_user_pages from pinning device pages. And by "pin", I think migrate_vma_check_page is not talking about FOLL_PIN, but any get_user_pages call. As far as I can tell, there should be nothing fundamentally wrong with pinning device pages for a short time. But I think we'll want to avoid FOLL_LONGTERM because that would affect our memory manager's ability to evict device memory.
Right, so long as my fix goes in I don't think there is anything wrong with pinning device public pages. Agree that we should avoid FOLL_LONGTERM pins for device memory though. I think the way to do that is update is_pinnable_page() so we treat device pages the same as other unpinnable pages ie. long-term pins will migrate the page.
In the case of device-private pages this is enforced by the fact they never have present pte's, so any attempt to GUP them results in a fault. But if I'm understanding this series correctly that won't be the case for coherent device pages right?
Right.
Regards, Felix
return is_device_private_page(page);
return is_device_page(page);}
/* For file back page */
@@ -2791,7 +2791,7 @@ EXPORT_SYMBOL(migrate_vma_setup);
handle_pte_fault()do_anonymous_page()- to map in an anonymous zero page but the struct page will be a ZONE_DEVICE
- private page.
*/
- private or coherent page.
static void migrate_vma_insert_page(struct migrate_vma *migrate, unsigned long addr, @@ -2867,10 +2867,15 @@ static void migrate_vma_insert_page(struct migrate_vma *migrate, swp_entry = make_readable_device_private_entry( page_to_pfn(page)); entry = swp_entry_to_pte(swp_entry);
} else if (is_device_page(page)) {How about adding an explicit `is_device_coherent_page()` helper? It would make the test more explicit that this is expected to handle just coherent pages and I bet there will be future changes that need to differentiate between private and coherent pages anyway.
entry = pte_mkold(mk_pte(page,READ_ONCE(vma->vm_page_prot)));if (vma->vm_flags & VM_WRITE)entry = pte_mkwrite(pte_mkdirty(entry));
* For now we only support migrating to un-addressable* device memory.
* We support migrating to private and coherent types* for device zone memory. */ pr_warn_once("Unsupported ZONE_DEVICE page type.\n"); goto abort;@@ -2976,10 +2981,10 @@ void migrate_vma_pages(struct migrate_vma *migrate) mapping = page_mapping(page);
if (is_zone_device_page(newpage)) {
if (is_device_private_page(newpage)) {
if (is_device_page(newpage)) { /*
* For now only support private anonymous when* migrating to un-addressable device memory.
* For now only support private and coherent* anonymous when migrating to device memory. */ if (mapping) { migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;