On Thu, Dec 03, 2020 at 02:25:20PM -0800, Yang Shi wrote: > On Thu, Dec 3, 2020 at 12:09 PM Roman Gushchin <[email protected]> wrote: > > > > On Wed, Dec 02, 2020 at 08:59:40PM -0800, Yang Shi wrote: > > > On Wed, Dec 2, 2020 at 7:01 PM Roman Gushchin <[email protected]> wrote: > > > > > > > > On Wed, Dec 02, 2020 at 10:27:20AM -0800, Yang Shi wrote: > > > > > Currently registered shrinker is indicated by non-NULL > > > > > shrinker->nr_deferred. > > > > > This approach is fine with nr_deferred atthe shrinker level, but the > > > > > following > > > > > patches will move MEMCG_AWARE shrinkers' nr_deferred to memcg level, > > > > > so their > > > > > shrinker->nr_deferred would always be NULL. This would prevent the > > > > > shrinkers > > > > > from unregistering correctly. > > > > > > > > > > Introduce a new "state" field to indicate if shrinker is registered > > > > > or not. > > > > > We could use the highest bit of flags, but it may be a little bit > > > > > complicated to > > > > > extract that bit and the flags is accessed frequently by vmscan > > > > > (every time shrinker > > > > > is called). So add a new field in "struct shrinker", we may waster a > > > > > little bit > > > > > memory, but it should be very few since there should be not too many > > > > > registered > > > > > shrinkers on a normal system. > > > > > > > > > > Signed-off-by: Yang Shi <[email protected]> > > > > > --- > > > > > include/linux/shrinker.h | 4 ++++ > > > > > mm/vmscan.c | 13 +++++++++---- > > > > > 2 files changed, 13 insertions(+), 4 deletions(-) > > > > > > > > > > diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h > > > > > index 0f80123650e2..0bb5be88e41d 100644 > > > > > --- a/include/linux/shrinker.h > > > > > +++ b/include/linux/shrinker.h > > > > > @@ -35,6 +35,9 @@ struct shrink_control { > > > > > > > > > > #define SHRINK_STOP (~0UL) > > > > > #define SHRINK_EMPTY (~0UL - 1) > > > > > + > > > > > +#define SHRINKER_REGISTERED 0x1 > > > > > + > > > > > /* > > > > > * A callback you can register to apply pressure to ageable caches. > > > > > * > > > > > @@ -66,6 +69,7 @@ struct shrinker { > > > > > long batch; /* reclaim batch size, 0 = default */ > > > > > int seeks; /* seeks to recreate an obj */ > > > > > unsigned flags; > > > > > + unsigned state; > > > > > > > > Hm, can't it be another flag? It seems like we have a plenty of free > > > > bits. > > > > > > I thought about this too. But I was not convinced by myself that > > > messing flags with state is a good practice. We may add more flags in > > > the future, so we may end up having something like: > > > > > > flag > > > flag > > > flag > > > state > > > flag > > > flag > > > ... > > > > > > Maybe we could use the highest bit for state? > > > > Or just > > state > > flag > > flag > > flag > > flag > > flag > > ... > > > > ? > > It is fine too. We should not add more states in foreseeable future.
It's always possible to shuffle things around for cleanup later on, too. We don't have to provide binary compatibility for existing flags, and changing a couple of adjacent bits isn't a big deal to keep things neat. Or am I missing something?
