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09:58:20PM +0800, Qi Zheng wrote: > From: Muchun Song > > In the near future, a folio will no longer pin its corresponding > memory cgroup. To ensure safety, it will only be appropriate to > hold the rcu read lock or acquire a reference to the memory cgroup > returned by folio_memcg(), thereby preventing it from being released. > > In the current patch, the rcu read lock is employed to safeguard > against the release of the memory cgroup in get_mem_cgroup_from_folio(). > > This serves as a preparatory measure for the reparenting of the > LRU pages. > > Signed-off-by: Muchun Song > Signed-off-by: Qi Zheng > --- This patch looks correct to me, so: Reviewed-by: Harry Yoo with a few side question on current implementation rather than this change... > mm/memcontrol.c | 11 ++++++++--- > 1 file changed, 8 insertions(+), 3 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index d484b632c790f..1da3ad77054d3 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -973,14 +973,19 @@ struct mem_cgroup *get_mem_cgroup_from_current(void) > */ > struct mem_cgroup *get_mem_cgroup_from_folio(struct folio *folio) > { > - struct mem_cgroup *memcg = folio_memcg(folio); > + struct mem_cgroup *memcg; > > if (mem_cgroup_disabled()) > return NULL; > > + if (!folio_memcg_charged(folio)) > + return root_mem_cgroup; > + > rcu_read_lock(); > - if (!memcg || WARN_ON_ONCE(!css_tryget(&memcg->css))) I have no idea why we're already calling rcu_read_lock() when a folio pins the memcg :) > - memcg = root_mem_cgroup; > +retry: > + memcg = folio_memcg(folio); > + if (unlikely(!css_tryget(&memcg->css))) > + goto retry; > rcu_read_unlock(); > return memcg; > } > -- > 2.20.1 -- Cheers, Harry / Hyeonggon