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charset="UTF-8" X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Dec 2, 2020 at 7:01 PM Roman Gushchin 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 > > --- > > 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? > > > > > /* These are for internal use */ > > struct list_head list; > > diff --git a/mm/vmscan.c b/mm/vmscan.c > > index 457ce04eebf2..0d628299e55c 100644 > > --- a/mm/vmscan.c > > +++ b/mm/vmscan.c > > @@ -378,6 +378,7 @@ void register_shrinker_prepared(struct shrinker *shrinker) > > if (shrinker->flags & SHRINKER_MEMCG_AWARE) > > idr_replace(&shrinker_idr, shrinker, shrinker->id); > > #endif > > + shrinker->state |= SHRINKER_REGISTERED; > > up_write(&shrinker_rwsem); > > } > > > > @@ -397,13 +398,17 @@ EXPORT_SYMBOL(register_shrinker); > > */ > > void unregister_shrinker(struct shrinker *shrinker) > > { > > - if (!shrinker->nr_deferred) > > - return; > > - if (shrinker->flags & SHRINKER_MEMCG_AWARE) > > - unregister_memcg_shrinker(shrinker); > > down_write(&shrinker_rwsem); > > + if (!shrinker->state) { > > + up_write(&shrinker_rwsem); > > + return; > > + } > > list_del(&shrinker->list); > > + shrinker->state &= ~SHRINKER_REGISTERED; > > up_write(&shrinker_rwsem); > > + > > + if (shrinker->flags & SHRINKER_MEMCG_AWARE) > > + unregister_memcg_shrinker(shrinker); > > kfree(shrinker->nr_deferred); > > shrinker->nr_deferred = NULL; > > } > > -- > > 2.26.2 > >