On 02.05.23 14:40, Peter Zijlstra wrote:
On Tue, May 02, 2023 at 02:08:10PM +0200, Peter Zijlstra wrote:
if (folio_test_anon(folio))
return true;
This relies on the mapping so belongs below the lockdep assert imo.
Oh, right you are.
/*
* Having IRQs disabled (as per GUP-fast) also inhibits RCU
* grace periods from making progress, IOW. they imply
* rcu_read_lock().
*/
lockdep_assert_irqs_disabled();
/*
* Inodes and thus address_space are RCU freed and thus safe to
* access at this point.
*/
mapping = folio_mapping(folio);
if (mapping && shmem_mapping(mapping))
return true;
return false;
+}
So arguably you should do *one* READ_ONCE() load of mapping and
consistently use that, this means open-coding both folio_test_anon() and
folio_mapping().
Open-coding folio_test_anon() should not be required. We only care about
PAGE_MAPPING_FLAGS stored alongside folio->mapping, that will stick
around until the anon page was freed.
@Lorenzo, you might also want to special-case hugetlb directly using
folio_test_hugetlb().
--
Thanks,
David / dhildenb
