Re: [PATCH net-next 1/2] net: Keep sk->sk_forward_alloc as a proper size

Shakeel Butt
2023-05-11T16:24:06Z

On Thu, May 11, 2023 at 2:27 AM Zhang, Cathy <cathy.zhang@intel.com> wrote:
>
>
>
[...]
>
> Here is the output with the command you paste, it's from system wide,
> I only show pieces of memcached records, and it seems to be a
> callee -> caller stack trace:
>
> 9.02% mc-worker [kernel.vmlinux] [k] page_counter_try_charge
> |
> --9.00%--page_counter_try_charge
> |
> --9.00%--try_charge_memcg
> mem_cgroup_charge_skmem
> |
> --9.00%--__sk_mem_raise_allocated
> __sk_mem_schedule
> |
> |--5.32%--tcp_try_rmem_schedule
> | tcp_data_queue
> | tcp_rcv_established
> | tcp_v4_do_rcv
> | tcp_v4_rcv
> | ip_protocol_deliver_rcu
> | ip_local_deliver_finish
> | ip_local_deliver
> | ip_rcv
> | __netif_receive_skb_one_core
> | __netif_receive_skb
> | process_backlog
> | __napi_poll
> | net_rx_action
> | __do_softirq
> | |
> | --5.32%--do_softirq.part.0
> | __local_bh_enable_ip
> | __dev_queue_xmit
> | ip_finish_output2
> | __ip_finish_output
> | ip_finish_output
> | ip_output
> | ip_local_out
> | __ip_queue_xmit
> | ip_queue_xmit
> | __tcp_transmit_skb
> | tcp_write_xmit
> | __tcp_push_pending_frames
> | tcp_push
> | tcp_sendmsg_locked
> | tcp_sendmsg
> | inet_sendmsg
> | sock_sendmsg
> | ____sys_sendmsg
>
> 8.98% mc-worker [kernel.vmlinux] [k] page_counter_cancel
> |
> --8.97%--page_counter_cancel
> |
> --8.97%--page_counter_uncharge
> drain_stock
> __refill_stock
> refill_stock
> |
> --8.91%--try_charge_memcg
> mem_cgroup_charge_skmem
> |
> --8.91%--__sk_mem_raise_allocated
> __sk_mem_schedule
> |
> |--5.41%--tcp_try_rmem_schedule
> | tcp_data_queue
> | tcp_rcv_established
> | tcp_v4_do_rcv
> | tcp_v4_rcv
> | ip_protocol_deliver_rcu
> | ip_local_deliver_finish
> | ip_local_deliver
> | ip_rcv
> | __netif_receive_skb_one_core
> | __netif_receive_skb
> | process_backlog
> | __napi_poll
> | net_rx_action
> | __do_softirq
> | do_softirq.part.0
> | __local_bh_enable_ip
> | __dev_queue_xmit
> | ip_finish_output2
> | __ip_finish_output
> | ip_finish_output
> | ip_output
> | ip_local_out
> | __ip_queue_xmit
> | ip_queue_xmit
> | __tcp_transmit_skb
> | tcp_write_xmit
> | __tcp_push_pending_frames
> | tcp_push
> | tcp_sendmsg_locked
> | tcp_sendmsg
> | inet_sendmsg
>
> 8.78% mc-worker [kernel.vmlinux] [k] try_charge_memcg
> |
> --8.77%--try_charge_memcg
> |
> --8.76%--mem_cgroup_charge_skmem
> |
> --8.76%--__sk_mem_raise_allocated
> __sk_mem_schedule
> |
> |--5.21%--tcp_try_rmem_schedule
> | tcp_data_queue
> | tcp_rcv_established
> | tcp_v4_do_rcv
> | |
> | --5.21%--tcp_v4_rcv
> | ip_protocol_deliver_rcu
> | ip_local_deliver_finish
> | ip_local_deliver
> | ip_rcv
> | __netif_receive_skb_one_core
> | __netif_receive_skb
> | process_backlog
> | __napi_poll
> | net_rx_action
> | __do_softirq
> | |
> | --5.21%--do_softirq.part.0
> | __local_bh_enable_ip
> | __dev_queue_xmit
> | ip_finish_output2
> | __ip_finish_output
> | ip_finish_output
> | ip_output
> | ip_local_out
> | __ip_queue_xmit
> | ip_queue_xmit
> | __tcp_transmit_skb
> | tcp_write_xmit
> | __tcp_push_pending_frames
> | tcp_push
> | tcp_sendmsg_locked
> | tcp_sendmsg
> | inet_sendmsg
> | sock_sendmsg
> | ____sys_sendmsg
> | ___sys_sendmsg
> | __sys_sendmsg
>
>
> >

I am suspecting we are doing a lot of charging for a specific memcg on
one CPU (or a set of CPUs) and a lot of uncharging on the different
CPU (or a different set of CPUs) and thus both of these code paths are
hitting the slow path a lot.

Eric, I remember we have an optimization in the networking stack that
tries to free the memory on the same CPU where the allocation
happened. Is that optimization enabled for this code path? Or maybe we
should do something similar in memcg code (with the assumption that my
suspicion is correct).