On 22.02.24 11:19, David Hildenbrand wrote:
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.
Thinking about it, your change will not only affect THP, but any call to
free_swap_and_cache().
Likely that's not what we want. :/
--
Cheers,
David / dhildenb
