On 03.07.2018 20:58, Matthew Wilcox wrote: > On Tue, Jul 03, 2018 at 06:46:57PM +0300, Kirill Tkhai wrote: >> shrinker_idr now contains only memcg-aware shrinkers, so all bits from memcg map >> may be potentially populated. In case of memcg-aware shrinkers and !memcg-aware >> shrinkers share the same numbers like you suggest, this will lead to increasing >> size of memcg maps, which is bad for memory consumption. So, memcg-aware shrinkers >> should to have its own IDR and its own numbers. The tricks like allocation big >> IDs for !memcg-aware shrinkers seem bad for me, since they make the code more >> complicated. > > Do we really have so very many !memcg-aware shrinkers? > > $ git grep -w register_shrinker |wc > 32 119 2221 > $ git grep -w register_shrinker_prepared |wc > 4 13 268 > (that's an overstatement; one of those is the declaration, one the definition, > and one an internal call, so we actually only have one caller of _prepared). > > So it looks to me like your average system has one shrinker per > filesystem, one per graphics card, one per raid5 device, and a few > miscellaneous. I'd be shocked if anybody had more than 100 shrinkers > registered on their laptop. > > I think we should err on the side of simiplicity and just have one IDR for > every shrinker instead of playing games to solve a theoretical problem. It just a standard situation for the systems with many containers. Every mount introduce a new shrinker to the system, so it's easy to see a system with 100 or ever 1000 shrinkers. AFAIR, Shakeel said he also has the similar configurations. So, this problem is not theoretical, it's just a standard situation for active consumer or Docker/etc. >>> This will actually reduce the size of each shrinker and be more >>> cache-efficient when calling the shrinkers. I think we can also get >>> rid of the shrinker_rwsem eventually, but let's leave it for now. >> >> This patchset does not make the cache-efficient bad, since without the patchset the situation >> is so bad, that it's just impossible to talk about the cache efficiently, >> so let's leave lockless iteration/etc for the future works. > > The situation is that bad /for your use case/. Not so much for others. > You're introducing additional complexity here, and it'd be nice if we > can remove some of the complexity that's already there. You started from cache-efficienty, and now you moved to existing complexity. I did some cleanups in this patchset, also there is Vladimir's patch, which simplifies shrinker logic. Also there is already 17 patches. Which already existing complexity you want to remove? I don't think there is existing complexity directly connected to this patchset.
