netdev - Re: [PATCH net-next 0/7] net: reduce tcp_memory

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Date:   Thu, 9 Jun 2022 09:33:53 -0400
From:   Soheil Hassas Yeganeh <soheil@...gle.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        netdev <netdev@...r.kernel.org>, Wei Wang <weiwan@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Neal Cardwell <ncardwell@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH net-next 0/7] net: reduce tcp_memory_allocated inflation

On Thu, Jun 9, 2022 at 2:34 AM Eric Dumazet <eric.dumazet@...il.com> wrote:
>
> From: Eric Dumazet <edumazet@...gle.com>
>
> Hosts with a lot of sockets tend to hit so called TCP memory pressure,
> leading to very bad TCP performance and/or OOM.
>
> The problem is that some TCP sockets can hold up to 2MB of 'forward
> allocations' in their per-socket cache (sk->sk_forward_alloc),
> and there is no mechanism to make them relinquish their share
> under mem pressure.
> Only under some potentially rare events their share is reclaimed,
> one socket at a time.
>
> In this series, I implemented a per-cpu cache instead of a per-socket one.
>
> Each CPU has a +1/-1 MB (256 pages on x86) forward alloc cache, in order
> to not dirty tcp_memory_allocated shared cache line too often.
>
> We keep sk->sk_forward_alloc values as small as possible, to meet
> memcg page granularity constraint.
>
> Note that memcg already has a per-cpu cache, although MEMCG_CHARGE_BATCH
> is defined to 32 pages, which seems a bit small.
>
> Note that while this cover letter mentions TCP, this work is generic
> and supports TCP, UDP, DECNET, SCTP.
>
> Eric Dumazet (7):
>   Revert "net: set SK_MEM_QUANTUM to 4096"
>   net: remove SK_MEM_QUANTUM and SK_MEM_QUANTUM_SHIFT
>   net: add per_cpu_fw_alloc field to struct proto
>   net: implement per-cpu reserves for memory_allocated
>   net: fix sk_wmem_schedule() and sk_rmem_schedule() errors
>   net: keep sk->sk_forward_alloc as small as possible
>   net: unexport __sk_mem_{raise|reduce}_allocated

Acked-by: Soheil Hassas Yeganeh <soheil@...gle.com>

Very nice work! Thank you for scaling up TCP again!

>  include/net/sock.h           | 100 +++++++++++++++--------------------
>  include/net/tcp.h            |   2 +
>  include/net/udp.h            |   1 +
>  net/core/datagram.c          |   3 --
>  net/core/sock.c              |  22 ++++----
>  net/decnet/af_decnet.c       |   4 ++
>  net/ipv4/tcp.c               |  13 ++---
>  net/ipv4/tcp_input.c         |   6 +--
>  net/ipv4/tcp_ipv4.c          |   3 ++
>  net/ipv4/tcp_output.c        |   2 +-
>  net/ipv4/tcp_timer.c         |  19 ++-----
>  net/ipv4/udp.c               |  14 +++--
>  net/ipv4/udplite.c           |   3 ++
>  net/ipv6/tcp_ipv6.c          |   3 ++
>  net/ipv6/udp.c               |   3 ++
>  net/ipv6/udplite.c           |   3 ++
>  net/iucv/af_iucv.c           |   2 -
>  net/mptcp/protocol.c         |  13 +++--
>  net/sctp/protocol.c          |   4 +-
>  net/sctp/sm_statefuns.c      |   2 -
>  net/sctp/socket.c            |  12 +++--
>  net/sctp/stream_interleave.c |   2 -
>  net/sctp/ulpqueue.c          |   4 --
>  23 files changed, 114 insertions(+), 126 deletions(-)
>
> --
> 2.36.1.255.ge46751e96f-goog
>