Re: [PATCH v4 1/3] mm: swap: move LRU insertion out of the swap cache allocator

[Kairui Song]

On Fri, Sep 11, 2026 at 5:47 PM Alexandre Ghiti <alex@xxxxxxxx> wrote:
>
> This is a preparatory patch.
>
> __swap_cache_alloc_folio() adds the new folio to the LRU itself, which

I think you mean:
"swap_cache_alloc_folio() adds the new folio to the LRU itself"

__swap_cache_alloc_folio is the new name you introduced in this patch.

> leaves its callers no way to act on the folio before it becomes visible
> to reclaim.  Two users need exactly that:
>
>  - moving the refault evaluation out of the swap cache folio allocation
>    requires it to happen before folio_add_lru(): that consumes PG_active
>    to file the folio on the inactive or the active list, and under MGLRU
>    it also reads PG_workingset to pick the generation.  Setting either
>    flag afterwards does not move the folio;
>
>  - zswap writeback dropbehind needs the buffer folio to stay off the LRU
>    entirely, as the per-CPU LRU batch would hold a reference on it and
>    keep remove_mapping() from freeing it once writeback completes.
>
> Defer the LRU insertion to the callers of __swap_cache_alloc_folio():

And you defer the LRU insertion and and rename the helper.

> each of them adds the folio right after the allocation, so there is no
> functional change intended.
>
> Suggested-by: Kairui Song <kasong@xxxxxxxxxxx>
> Reviewed-by: Nhat Pham <nphamcs@xxxxxxxxx>
> Reviewed-by: Kunwu Chan <kunwu.chan@xxxxxxxxx>
> Acked-by: Usama Arif <usama.arif@xxxxxxxxx>
> Signed-off-by: Alexandre Ghiti <alex@xxxxxxxx>
> ---
>  mm/swap.h       |  6 +++---
>  mm/swap_state.c | 20 ++++++++++++--------
>  mm/swapfile.c   |  2 +-
>  mm/zswap.c      |  5 +++--
>  4 files changed, 19 insertions(+), 14 deletions(-)

Everything else looks good.

Reviewed-by: Kairui Song <kasong@xxxxxxxxxxx>