On Tue 02-01-24 10:21:44, Dan Schatzberg wrote: > 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. I do agree with this. Especially for an opt-in features it is better if the default initialization has a clear meanining. In this case even if somebody doesn't use the helper then the NULL should be caught as NULL ptr rather than a silent misbehavior. -- Michal Hocko SUSE Labs
