netdev - RE: [PATCH net-next 1/2] net: Keep sk->sk_forward

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Date: Wed, 10 May 2023 13:52:16 +0000
From: "Zhang, Cathy" <cathy.zhang@...el.com>
To: Eric Dumazet <edumazet@...gle.com>
CC: Shakeel Butt <shakeelb@...gle.com>, Linux MM <linux-mm@...ck.org>, Cgroups
	<cgroups@...r.kernel.org>, Paolo Abeni <pabeni@...hat.com>,
	"davem@...emloft.net" <davem@...emloft.net>, "kuba@...nel.org"
	<kuba@...nel.org>, "Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
	"Srinivas, Suresh" <suresh.srinivas@...el.com>, "Chen, Tim C"
	<tim.c.chen@...el.com>, "You, Lizhen" <lizhen.you@...el.com>,
	"eric.dumazet@...il.com" <eric.dumazet@...il.com>, "netdev@...r.kernel.org"
	<netdev@...r.kernel.org>
Subject: RE: [PATCH net-next 1/2] net: Keep sk->sk_forward_alloc as a proper
 size



> -----Original Message-----
> From: Eric Dumazet <edumazet@...gle.com>
> Sent: Wednesday, May 10, 2023 7:25 PM
> To: Zhang, Cathy <cathy.zhang@...el.com>
> Cc: Shakeel Butt <shakeelb@...gle.com>; Linux MM <linux-mm@...ck.org>;
> Cgroups <cgroups@...r.kernel.org>; Paolo Abeni <pabeni@...hat.com>;
> davem@...emloft.net; kuba@...nel.org; Brandeburg, Jesse
> <jesse.brandeburg@...el.com>; Srinivas, Suresh
> <suresh.srinivas@...el.com>; Chen, Tim C <tim.c.chen@...el.com>; You,
> Lizhen <lizhen.you@...el.com>; eric.dumazet@...il.com;
> netdev@...r.kernel.org
> Subject: Re: [PATCH net-next 1/2] net: Keep sk->sk_forward_alloc as a proper
> size
> 
> On Wed, May 10, 2023 at 1:11 PM Zhang, Cathy <cathy.zhang@...el.com>
> wrote:
> >
> > Hi Shakeel, Eric and all,
> >
> > How about adding memory pressure checking in sk_mem_uncharge() to
> > decide if keep part of memory or not, which can help avoid the issue
> > you fixed and the problem we find on the system with more CPUs.
> >
> > The code draft is like this:
> >
> > static inline void sk_mem_uncharge(struct sock *sk, int size) {
> >         int reclaimable;
> >         int reclaim_threshold = SK_RECLAIM_THRESHOLD;
> >
> >         if (!sk_has_account(sk))
> >                 return;
> >         sk->sk_forward_alloc += size;
> >
> >         if (mem_cgroup_sockets_enabled && sk->sk_memcg &&
> >             mem_cgroup_under_socket_pressure(sk->sk_memcg)) {
> >                 sk_mem_reclaim(sk);
> >                 return;
> >         }
> >
> >         reclaimable = sk->sk_forward_alloc -
> > sk_unused_reserved_mem(sk);
> >
> >         if (reclaimable > reclaim_threshold) {
> >                 reclaimable -= reclaim_threshold;
> >                 __sk_mem_reclaim(sk, reclaimable);
> >         }
> > }
> >
> > I've run a test with the new code, the result looks good, it does not
> > introduce latency, RPS is the same.
> >
> 
> It will not work for sockets that are idle, after a burst.
> If we restore per socket caches, we will need a shrinker.
> Trust me, we do not want that kind of big hammer, crushing latencies.
> 
> Have you tried to increase batch sizes ?

I jus picked up 256 and 1024 for a try, but no help, the overhead still exists.

> 
> Any kind of cache (even per-cpu) might need some adjustment when core
> count or expected traffic is increasing.
> This was somehow hinted in
> commit 1813e51eece0ad6f4aacaeb738e7cced46feb470
> Author: Shakeel Butt <shakeelb@...gle.com>
> Date:   Thu Aug 25 00:05:06 2022 +0000
> 
>     memcg: increase MEMCG_CHARGE_BATCH to 64
> 
> 
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index
> 222d7370134c73e59fdbdf598ed8d66897dbbf1d..0418229d30c25d114132a1e
> d46ac01358cf21424
> 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -334,7 +334,7 @@ struct mem_cgroup {
>   * TODO: maybe necessary to use big numbers in big irons or dynamic based
> of the
>   * workload.
>   */
> -#define MEMCG_CHARGE_BATCH 64U
> +#define MEMCG_CHARGE_BATCH 128U
> 
>  extern struct mem_cgroup *root_mem_cgroup;
> 
> diff --git a/include/net/sock.h b/include/net/sock.h index
> 656ea89f60ff90d600d16f40302000db64057c64..82f6a288be650f886b207e6a
> 5e62a1d5dda808b0
> 100644
> --- a/include/net/sock.h
> +++ b/include/net/sock.h
> @@ -1433,8 +1433,8 @@ sk_memory_allocated(const struct sock *sk)
>         return proto_memory_allocated(sk->sk_prot);
>  }
> 
> -/* 1 MB per cpu, in page units */
> -#define SK_MEMORY_PCPU_RESERVE (1 << (20 - PAGE_SHIFT))
> +/* 2 MB per cpu, in page units */
> +#define SK_MEMORY_PCPU_RESERVE (1 << (21 - PAGE_SHIFT))
> 
>  static inline void
>  sk_memory_allocated_add(struct sock *sk, int amt)
> 
> 
> 
> 
> 
> 
> > > -----Original Message-----
> > > From: Shakeel Butt <shakeelb@...gle.com>
> > > Sent: Wednesday, May 10, 2023 12:10 AM
> > > To: Eric Dumazet <edumazet@...gle.com>; Linux MM <linux-
> > > mm@...ck.org>; Cgroups <cgroups@...r.kernel.org>
> > > Cc: Zhang, Cathy <cathy.zhang@...el.com>; Paolo Abeni
> > > <pabeni@...hat.com>; davem@...emloft.net; kuba@...nel.org;
> > > Brandeburg, Jesse <jesse.brandeburg@...el.com>; Srinivas, Suresh
> > > <suresh.srinivas@...el.com>; Chen, Tim C <tim.c.chen@...el.com>;
> > > You, Lizhen <lizhen.you@...el.com>; eric.dumazet@...il.com;
> > > netdev@...r.kernel.org
> > > Subject: Re: [PATCH net-next 1/2] net: Keep sk->sk_forward_alloc as
> > > a proper size
> > >
> > > +linux-mm & cgroup
> > >
> > > Thread: https://lore.kernel.org/all/20230508020801.10702-1-
> > > cathy.zhang@...el.com/
> > >
> > > On Tue, May 9, 2023 at 8:43 AM Eric Dumazet <edumazet@...gle.com>
> > > wrote:
> > > >
> > > [...]
> > > > Some mm experts should chime in, this is not a networking issue.
> > >
> > > Most of the MM folks are busy in LSFMM this week. I will take a look
> > > at this soon.