Hi Yu Zhao, Thanks for the feedback, sorry for the delayed response. On Thu, Dec 21, 2023 at 10:31:59PM -0700, Yu Zhao wrote: > On Wed, Dec 20, 2023 at 8:27 AM Dan Schatzberg <schatzberg.dan@xxxxxxxxx> wrote: > > > > ... > > The cover letter says: > "Previously, this exact interface addition was proposed by Yosry[3]." > > So I think it should be acknowledged with a Suggested-by, based on: > "A Suggested-by: tag indicates that the patch idea is suggested by the > person named and ensures credit to the person for the idea." > from > https://docs.kernel.org/process/submitting-patches.html#using-reported-by-tested-by-reviewed-by-suggested-by-and-fixes Sure, will do. > > diff --git a/mm/vmscan.c b/mm/vmscan.c > > index d91963e2d47f..aa5666842c49 100644 > > --- a/mm/vmscan.c > > +++ b/mm/vmscan.c > > @@ -92,6 +92,9 @@ struct scan_control { > > unsigned long anon_cost; > > unsigned long file_cost; > > > > + /* Swappiness value for reclaim. NULL will fall back to per-memcg/global value */ > > + int *swappiness; > > Using a pointer to indicate whether the type it points to is > overridden isn't really a good practice. > > A better alternative was suggested during the v2: > "Perhaps the negative to avoid unnecessary dereferences." > https://lore.kernel.org/linux-mm/dhhjw4h22q4ngwtxmhuyifv32zjd6z2relrcjgnxsw6zys3mod@o6dh5dy53ae3/ I did have a couple versions with a negative but it creates initialization issues where every instantiation of scan_control needs to make sure to initialize swappiness or else it will behave as if swappiness is 0. That's pretty error prone so using the pointer seemed the better approach. > Since only proactive reclaim can override swappiness, meaning it only > happens if sc->proactive is true, I think the best way to make it work > without spending much effort is create a helper as Michal suggest but > it should look like: > > sc_swappiness() > { > return sc->proactive ? sc->swappiness : mem_cgroup_swappiness(memcg); > } > > In this patchset, sc->swappiness really means > sc->proactive_swappiness. So it should be renamed accordingly. Helper aside, I disagree with this point about coupling with the proactive flag. The fact that the only user currently is proactive reclaim doesn't imply to me that the interface (in scan_control) should be coupled to the use-case. It's easier to reason about a swappiness field that overrides swappiness for all scans that set it regardless of the users.
