On 5/20/24 4:30 PM, Matthew Wilcox wrote:
On Mon, May 20, 2024 at 03:44:07PM -0700, Sidhartha Kumar wrote:
All users have been converted to use the folio version of these macros,
we can safely remove the page based interface.
Yay!
Reviewed-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
There is only one remaining user of page-based Test version of these macros.
in mm/memory-hotplug.c:
if (!PageHuge(page))
continue;
head = compound_head(page);
/*
* This test is racy as we hold no reference or lock. The
* hugetlb page could have been free'ed and head is no longer
* a hugetlb page before the following check. In such unlikely
* cases false positives and negatives are possible. Calling
* code must deal with these scenarios.
*/
if (HPageMigratable(head))
goto found;
skip = compound_nr(head) - (pfn - page_to_pfn(head));
I've previously sent a patch to convert this to folios[1] but got feedback that
it was unsafe. But I'm not sure why replacing compound_head() with page_folio()
and using folio_test_hugetlb_migratable(folio) rather than HPageMigratable(head)
changes the existing behavior. With no reference or lock, can't the head pointer
also be moved and no longer be a part of page like the comment states. So would
the folio conversion just be maintaining this level of existing un-safety that
the calling code should handle anyways?
[1]:
https://lore.kernel.org/lkml/Y89DK23hYiLtgGNk@xxxxxxxxxxxxxxxxxxxx/T/#mb3a339b98386b1cd0b87f94f45163756ebd7feaa
