Re: [PATCH v5 09/14] mm/mglru: use the common routine for dirty/writeback reactivation

[Barry Song]

On Mon, Apr 13, 2026 at 12:48 AM Kairui Song via B4 Relay
<devnull+kasong.tencent.com@xxxxxxxxxx> wrote:
>
> From: Kairui Song <kasong@xxxxxxxxxxx>
>
> Currently MGLRU will move the dirty writeback folios to the second
> oldest gen instead of reactivate them like the classical LRU. This
> might help to reduce the LRU contention as it skipped the isolation.
> But as a result we will see these folios at the LRU tail more frequently
> leading to inefficient reclaim.
>
> Besides, the dirty / writeback check after isolation in
> shrink_folio_list is more accurate and covers more cases. So instead,
> just drop the special handling for dirty writeback, use the common
> routine and re-activate it like the classical LRU.
>
> This should in theory improve the scan efficiency. These folios will be
> rotated back to LRU tail once writeback is done so there is no risk of
> hotness inversion. And now each reclaim loop will have a higher
> success rate. This also prepares for unifying the writeback and
> throttling mechanism with classical LRU, we keep these folios far from
> tail so detecting the tail batch will have a similar pattern with
> classical LRU.
>
> The micro optimization that avoids LRU contention by skipping the
> isolation is gone, which should be fine. Compared to IO and writeback
> cost, the isolation overhead is trivial.
>
> And using the common routine also keeps the folio's referenced bits
> (tier bits), which could improve metrics in the long term. Also no
> more need to clean reclaim bit as the common routine will make use
> of it.
>
> Note the common routine updates a few throttling and writeback counters,
> which are not used, and never have been for the MGLRU case. We will
> start making use of these in later commits.
>
> Reviewed-by: Axel Rasmussen <axelrasmussen@xxxxxxxxxx>
> Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>

I like the move to the common path, activating the folio and
relying on folio rotation afterwards. The original MGLRU code
seems over-designed and may hurt performance. It seems to
overthink things.

Reviewed-by: Barry Song <baohua@xxxxxxxxxx>