On 26.02.24 17:07, Matthew Wilcox wrote:
On Mon, Feb 26, 2024 at 03:13:23PM +0100, David Hildenbrand wrote:
+ xas_for_each(xas, folio, ULONG_MAX) {
+ if (!xa_is_value(folio) && memfd_folio_has_extra_refs(folio))
xas_set_mark(xas, MEMFD_TAG_PINNED);
... we decline to tag value entries here ...
@@ -95,20 +90,15 @@ static int memfd_wait_for_pins(struct address_space *mapping)
xas_set(&xas, 0);
xas_lock_irq(&xas);
- xas_for_each_marked(&xas, page, ULONG_MAX, MEMFD_TAG_PINNED) {
+ xas_for_each_marked(&xas, folio, ULONG_MAX, MEMFD_TAG_PINNED) {
bool clear = true;
- cache_count = 1;
- if (!xa_is_value(page) &&
- PageTransHuge(page) && !PageHuge(page))
- cache_count = HPAGE_PMD_NR;
-
- if (!xa_is_value(page) && cache_count !=
- page_count(page) - total_mapcount(page)) {
+ if (!xa_is_value(folio) &&
+ memfd_folio_has_extra_refs(folio)) {
... so we don't need to test it here because we'll never see any value
entries. No?
I was not able to convince myself that swapout code would clear the mark
when replacing the entry.
shmem_writepage()->shmem_delete_from_page_cache()->shmem_replace_entry()
will perform a xas_store() with swp_to_radix_entry(swap) under
xa_lock_irq().
Reading the doc, and staring at the code for a bit too long, I think
xas_store() would only clear tags when deleting an entry (passing NULL).
But maybe xas_store() will always clear tags?
In memfd code, I think we could see swapout between memfd_tag_pins() and
the check for tags, where we drop the xa_lock. Unless some other lock
(inode lock?) protects us.
Thanks!
--
Cheers,
David / dhildenb
