Re: [PATCH 00/13] mm: PMD-level swap entries for anonymous THPs

Usama Arif
2026-04-27T13:38:49Z

On 27/04/2026 11:01, Usama Arif wrote:
> When reclaim swaps out a PMD-mapped anonymous THP today, the PMD is
> split into 512 PTE-level swap entries via TTU_SPLIT_HUGE_PMD before
> unmap.
>
> This series introduces a PMD-level swap entry. The huge mapping is
> preserved across the swap round-trip, and do_huge_pmd_swap_page()
> resolves the entire 2 MB region in a single fault on swap-in,
> no khugepaged involvement is needed. swap_map metadata is identical
> either way (512 single-slot counts), so the PTE split buys nothing
> on the swap side, it is purely a page-table representation change.
>
> This work was brought about after Hugh reported that one of the
> major blockers for having lazy page table deposit is the lack of
> PMD swap entries [1]. However, this series has benefits of its
> own:

+Hugh. Hugh raised this in [1], and I completely forgot to add him
to the series, sorry about that!

[1] https://lore.kernel.org/all/6869b7f0-84e1-fb93-03f1-9442cdfe476b@google.com/