On Fri, Apr 17, 2020 at 9:54 AM Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > On Fri 17-04-20 09:41:04, Shakeel Butt wrote: > > On Fri, Apr 17, 2020 at 9:03 AM Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > > > > > On Fri 17-04-20 22:43:43, Alex Shi wrote: > > > > This patch fold MEMCG_SWAP feature into kernel as default function. That > > > > required a short size memcg id for each of page. As Johannes mentioned > > > > > > > > "the overhead of tracking is tiny - 512k per G of swap (0.04%).' > > > > > > > > So all swapout page could be tracked for its memcg id. > > > > > > I am perfectly OK with dropping the CONFIG_MEMCG_SWAP. The code that is > > > guarded by it is negligible and the resulting code is much easier to > > > read so no objection on that front. I just do not really see any real > > > reason to flip the default for cgroup v1. Why do we want/need that? > > > > > > > Yes, the changelog is lacking the motivation of this change. This is > > proposed by Johannes and I was actually expecting the patch from him. > > The motivation is to make the things simpler for per-memcg LRU locking > > and workingset for anon memory (Johannes has described these really > > well, lemme find the email). If we keep the differentiation between > > cgroup v1 and v2, then there is actually no point of this cleanup as > > per-memcg LRU locking and anon workingset still has to handle the > > !do_swap_account case. > > All those details really have to go into the changelog. I have to say > that I still do not understand why the actual accounting swap or not > makes any difference for per per-memcg LRU. Here is Johannes explanation: https://lore.kernel.org/linux-mm/20200413180725.GA99267@xxxxxxxxxxx/ > Especially when your patch You mean Alex's patch. > keeps the kernel command line parameter still in place. > > Anyway, it would be much more simpler to have a patch that drops the > CONFIG_MEMCG_SWAP and a separate one which switches the default > beahvior. I am not saying I am ok with the later but if the > justification is convincing then I might change my mind. > -- > Michal Hocko > SUSE Labs
