On Thu 02-07-20 18:35:31, Vlastimil Babka wrote: > On 7/2/20 6:22 PM, Michal Hocko wrote: > > On Wed 01-07-20 11:45:52, Roman Gushchin wrote: > > [...] > >> >From c97afecd32c0db5e024be9ba72f43d22974f5bcd Mon Sep 17 00:00:00 2001 > >> From: Roman Gushchin <guro@xxxxxx> > >> Date: Wed, 1 Jul 2020 11:05:32 -0700 > >> Subject: [PATCH] mm: kmem: make memcg_kmem_enabled() irreversible > >> > >> Historically the kernel memory accounting was an opt-in feature, which > >> could be enabled for individual cgroups. But now it's not true, and > >> it's on by default both on cgroup v1 and cgroup v2. And as long as a > >> user has at least one non-root memory cgroup, the kernel memory > >> accounting is on. So in most setups it's either always on (if memory > >> cgroups are in use and kmem accounting is not disabled), either always > >> off (otherwise). > >> > >> memcg_kmem_enabled() is used in many places to guard the kernel memory > >> accounting code. If memcg_kmem_enabled() can reverse from returning > >> true to returning false (as now), we can't rely on it on release paths > >> and have to check if it was on before. > >> > >> If we'll make memcg_kmem_enabled() irreversible (always returning true > >> after returning it for the first time), it'll make the general logic > >> more simple and robust. It also will allow to guard some checks which > >> otherwise would stay unguarded. > >> > >> Signed-off-by: Roman Gushchin <guro@xxxxxx> > > Fixes: ? or let Andrew squash it to some patch of your series (it's in mmotm I > think)? I would rather make it its own patch because this is really subtle. -- Michal Hocko SUSE Labs
