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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 Fri, Dec 4, 2020 at 10:54 AM Johannes Weiner wrote: > > On Thu, Dec 03, 2020 at 02:25:20PM -0800, Yang Shi wrote: > > On Thu, Dec 3, 2020 at 12:09 PM Roman Gushchin 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 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? > > > > > > 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? No. It is definitely not a big deal.