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No > > functional change. > > > > The swap charging path currently drops its RCU read lock after acquiring > > a private ID reference. This is safe because the ID reference pins the > > memcg's CSS. > > > > Moving private ID references to objcgs will remove that lifetime > > guarantee. Keep the RCU read lock held while accessing the memcg for > > counter charging, statistics and failure handling. (This matches what > > __memcg1_swapout() already does.). > > > > Save the private ID before dropping the RCU read lock, and use the saved > > value when recording the swap entry. The swap cluster locking remains > > outside the RCU read-side critical section. > > > > Signed-off-by: Bingfang Guo > > --- > > mm/memcontrol.c | 8 +++++--- > > 1 file changed, 5 insertions(+), 3 deletions(-) > > > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > > index 791e536efaebe..72522ec827c9a 100644 > > --- a/mm/memcontrol.c > > +++ b/mm/memcontrol.c > > @@ -5954,6 +5954,7 @@ int __mem_cgroup_try_charge_swap(struct folio *folio) > > struct page_counter *counter; > > struct mem_cgroup *memcg; > > struct obj_cgroup *objcg; > > + unsigned short private_id; > > > > if (do_memsw_account()) > > return 0; > > @@ -5973,20 +5974,21 @@ int __mem_cgroup_try_charge_swap(struct folio *folio) > > > > If there is one more spin of this patch, I think scoped_guard(rcu) would be more > readable here, so please use that here. > Hi, Shakeel. Thanks for your review and suggestion! It looks like a good idea. I will include that in the next version! > > memcg = mem_cgroup_private_id_get_online(memcg, nr_pages); > > /* memcg is pined by memcg ID. */ > > - rcu_read_unlock(); > > + private_id = mem_cgroup_private_id(memcg); > > > > if (!mem_cgroup_is_root(memcg) && > > !page_counter_try_charge(&memcg->swap, nr_pages, &counter)) { > > memcg_memory_event(memcg, MEMCG_SWAP_MAX); > > memcg_memory_event(memcg, MEMCG_SWAP_FAIL); > > mem_cgroup_private_id_put(memcg, nr_pages); > > + rcu_read_unlock(); > > return -ENOMEM; > > } > > mod_memcg_state(memcg, MEMCG_SWAP, nr_pages); > > + rcu_read_unlock(); > > > > ci = swap_cluster_get_and_lock(folio); > > - __swap_cgroup_set(ci, swp_cluster_offset(folio->swap), nr_pages, > > - mem_cgroup_private_id(memcg)); > > + __swap_cgroup_set(ci, swp_cluster_offset(folio->swap), nr_pages, private_id); > > swap_cluster_unlock(ci); > > > > return 0; > > > > -- > > 2.43.7 > > > >