Messages in this thread | | | Date | Mon, 20 Jun 2022 14:13:43 +0800 | From | Muchun Song <> | Subject | Re: [PATCH v5 07/11] mm: memcontrol: make all the callers of {folio,page}_memcg() safe |
| |
On Sun, Jun 19, 2022 at 12:37:32PM -0700, Roman Gushchin wrote: > On Mon, May 30, 2022 at 03:49:15PM +0800, Muchun Song wrote: > > When we use objcg APIs to charge the LRU pages, the page will not hold > > a reference to the memcg associated with the page. So the caller of the > > {folio,page}_memcg() should hold an rcu read lock or obtain a reference > > to the memcg associated with the page to protect memcg from being > > released. So introduce get_mem_cgroup_from_{page,folio}() to obtain a > > reference to the memory cgroup associated with the page. > > > > In this patch, make all the callers hold an rcu read lock or obtain a > > reference to the memcg to protect memcg from being released when the LRU > > pages reparented. > > > > We do not need to adjust the callers of {folio,page}_memcg() during > > the whole process of mem_cgroup_move_task(). Because the cgroup migration > > and memory cgroup offlining are serialized by @cgroup_mutex. In this > > routine, the LRU pages cannot be reparented to its parent memory cgroup. > > So {folio,page}_memcg() is stable and cannot be released. > > > > This is a preparation for reparenting the LRU pages. > > > > Signed-off-by: Muchun Song <songmuchun@bytedance.com> > > Acked-by: Roman Gushchin <roman.gushchin@linux.dev> >
Thanks for your review.
> The locking seems to be correct. I'm slightly worried about a potential > perf degradation, especially on dying cgroups, where css_get() is relatively > expensive. I hope getting it into mm-unstable will help to determine > whether it's actually a problem. >
I'll send a new version based on mm-unstable ASAP.
Thanks.
> Thanks! >
| |