On Tue 05-09-23 08:54:46, Yosry Ahmed wrote: > On Tue, Sep 5, 2023 at 7:10 AM Michal Koutný <mkoutny@xxxxxxxx> wrote: > > > > On Mon, Sep 04, 2023 at 05:41:10PM +0200, Michal Hocko <mhocko@xxxxxxxx> wrote: > > > So it also creates an undocumented but userspace visible behavior. > > > Something that userspace might start depending on, right? > > > > Yes but - > > - depending on undocumented behavior is a mistake, > > - breaking the dependency would manifest (in the case I imagine) as a > > performance regression (and if there are some users, the future can > > allow them configuring periodic kernel flush to compensate for that). > > I think I am missing something. This change basically makes userspace > readers (for the root memcg) help out unified flushers, which are > in-kernel readers (e.g. reclaim) -- not the other way around. > > How would that create a userspace visible behavior that a dependency > can be formed on? Users expecting reclaim to be faster right after > reading root stats? I would guess that would be too flaky to cause a > behavior that people can depend on tbh. Flaky or not, it might cause behavior difference and a subtle one. I can imagine nohz and similar workloads wanting to (ab)use this to reduce kernel footprint. If we really need this then make it obvious in the changelog at least. -- Michal Hocko SUSE Labs
