On 25.10.23 16:45, Ryan Roberts wrote:
As preparation for supporting small-sized THP in the swap-out path, without first needing to split to order-0, Remove the CLUSTER_FLAG_HUGE, which, when present, always implies PMD-sized THP, which is the same as the cluster size. The only use of the flag was to determine whether a swap entry refers to a single page or a PMD-sized THP in swap_page_trans_huge_swapped(). Instead of relying on the flag, we now pass in nr_pages, which originates from the folio's number of pages. This allows the logic to work for folios of any order. The one snag is that one of the swap_page_trans_huge_swapped() call sites does not have the folio. But it was only being called there to avoid bothering to call __try_to_reclaim_swap() in some cases. __try_to_reclaim_swap() gets the folio and (via some other functions) calls swap_page_trans_huge_swapped(). So I've removed the problematic call site and believe the new logic should be equivalent.
That is the __try_to_reclaim_swap() -> folio_free_swap() -> folio_swapped() -> swap_page_trans_huge_swapped() call chain I assume.
The "difference" is that you will now (1) get another temporary reference on the folio and (2) (try)lock the folio every time you discard a single PTE of a (possibly) large THP.
-- Cheers, David / dhildenb
