On Sat, Mar 23, 2024 at 12:41:36AM +1300, Barry Song wrote:
> Commit d0637c505f8a1 ("arm64: enable THP_SWAP for arm64") brings up
> THP_SWAP on ARM64, but it doesn't enable THP_SWP on hardware with
> MTE as the MTE code works with the assumption tags save/restore is
> always handling a folio with only one page.
>
> The limitation should be removed as more and more ARM64 SoCs have
> this feature. Co-existence of MTE and THP_SWAP becomes more and
> more important.
>
> This patch makes MTE tags saving support large folios, then we don't
> need to split large folios into base pages for swapping out on ARM64
> SoCs with MTE any more.
Can we go further than this patch and only support PG_mte_tagged and
PG_mte_lock on folio->flags instead of page->flags? We're down to using
page->flags for these two MTE bits, a whole lot of s390 junk, PG_hwpoison,
PG_head, PG_anon_exclusive and Zone/Section/Node/KASAN/last_cpupid.
Looking at some of the callers, the call in copy_highpage() would need
to be lifted to its caller so that we only set the tags once per folio
rather than try to set them per page of a folio ... might be a bit of
churn, and I'd hate to try to do it myself without being able to test it.
