On 2/23/24 10:37, Chengming Zhou wrote: > On 2024/2/23 17:24, Vlastimil Babka wrote: >> >>>> >>> >>> I think this is a better direction! We can use RCU list if slab can be freed by RCU. >> >> Often we remove slab from the partial list for other purposes than freeing - >> i.e. to become a cpu (partial) slab, and that can't be handled by a rcu >> callback nor can we wait a grace period in such situations. > > IMHO, only free_slab() need to use call_rcu() to delay free the slab, > other paths like taking partial slabs from node partial list don't need > to wait for RCU grace period. > > All we want is safely lockless iterate over the node partial list, right? Yes, and for that there's the "list_head slab_list", which is in union with "struct slab *next" and "int slabs" for the cpu partial list. So if we remove a slab from the partial list and rewrite the list_head for the partial list purposes, it will break the lockless iterators, right? We would have to wait a grace period between unlinking the slab from partial list (so no new iterators can reach it), and reusing the list_head (so we are sure the existing iterators stopped looking at our slab). Maybe there's more advanced rcu tricks but this is my basic understanding how this works. > Thanks.
