On Mon, Nov 09, 2020 at 05:06:15PM -0800, Roman Gushchin wrote: > Many kernel memory accounting paths are guarded by the > memcg_kmem_enabled_key static key. It changes it's state during > the onlining of the first non-root cgroup. However is doesn't > happen atomically: before all call sites will become patched > some charges/uncharges can be skipped, resulting in an unbalanced > charge. The problem is mostly a theoretical issue, unlikely > having a noticeable impact ion the real life. memcg_online_kmem() is called from .css_alloc rather than .css_online, at a time where memcg is brandnew and the css hasn't been set up and published yet (the refcount isn't even initialized for css_tryget()). I don't really see how charges could race with that. We may want to rename memcg_online_kmem() to memcg_alloc_kmem() or something. > Before the rework of the slab controller we relied at setting > kmemcg_id after enabling the memcg_kmem_enabled_key static key. > Now we can use the setting of memcg->objcg to enable the slab > memory accounting atomically. I suspect that code comment has been out of date since commit 0b8f73e104285a4badf9d768d1c39b06d77d1f97.
