Re: [PATCH 7/8] mm/mglru: simplify and improve dirty writeback handling

Baolin Wang
2026-03-26T07:56:31Z

On 3/18/26 3:09 AM, Kairui Song via B4 Relay wrote:
> From: Kairui Song <kasong@tencent.com>
>
> The current handling of dirty writeback folios is not working well for
> file page heavy workloads: Dirty folios are protected and move to next
> gen upon isolation of getting throttled or reactivated upon pageout
> (shrink_folio_list).
>
> This might help to reduce the LRU lock contention slightly, but as a
> result, the ping-pong effect of folios between head and tail of last two
> gens is serious as the shrinker will run into protected dirty writeback
> folios more frequently compared to activation. The dirty flush wakeup
> condition is also much more passive compared to active/inactive LRU.
> Active / inactve LRU wakes the flusher if one batch of folios passed to
> shrink_folio_list is unevictable due to under writeback, but MGLRU
> instead has to check this after the whole reclaim loop is done, and then
> count the isolation protection number compared to the total reclaim
> number.
>
> And we previously saw OOM problems with it, too, which were fixed but
> still not perfect [1].
>
> So instead, just drop the special handling for dirty writeback, just
> re-activate it like active / inactive LRU. And also move the dirty flush
> wake up check right after shrink_folio_list. This should improve both
> throttling and performance.

Make sense to me. Additionally, I think there is still room to improve
the writeback-related logic in shrink_folio_list().