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Message-ID: <588689343dcd6c904e7fc142a001043015e5b14e.camel@redhat.com>
Date: Tue, 09 May 2023 09:52:28 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Abel Wu <wuyun.abel@...edance.com>, "David S . Miller"
<davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
<kuba@...nel.org>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sock: Fix misuse of sk_under_memory_pressure()
On Sat, 2023-05-06 at 16:59 +0800, Abel Wu wrote:
> The commit 180d8cd942ce ("foundations of per-cgroup memory pressure
> controlling") wrapped proto::memory_pressure status into an accessor
> named sk_under_memory_pressure(), and in the next commit e1aab161e013
> ("socket: initial cgroup code") added the consideration of net-memcg
> pressure into this accessor.
>
> But with the former patch applied, not all of the call sites of
> sk_under_memory_pressure() are interested in net-memcg's pressure.
> The __sk_mem_{raise,reduce}_allocated() only focus on proto/netns
> pressure rather than net-memcg's.
Why do you state the above? The current behavior is established since
~12y, arguably we can state quite the opposite.
I think this patch should at least target net-next, and I think we need
a more detailed reasoning to introduce such behavior change.
> IOW this accessor are generally
> used for deciding whether should reclaim or not.
>
> Fixes: e1aab161e013 ("socket: initial cgroup code")
> Signed-off-by: Abel Wu <wuyun.abel@...edance.com>
> ---
> include/net/sock.h | 5 -----
> net/core/sock.c | 17 +++++++++--------
> 2 files changed, 9 insertions(+), 13 deletions(-)
>
> diff --git a/include/net/sock.h b/include/net/sock.h
> index 8b7ed7167243..752d51030c5a 100644
> --- a/include/net/sock.h
> +++ b/include/net/sock.h
> @@ -1404,11 +1404,6 @@ static inline int sk_under_cgroup_hierarchy(struct sock *sk,
> #endif
> }
>
> -static inline bool sk_has_memory_pressure(const struct sock *sk)
> -{
> - return sk->sk_prot->memory_pressure != NULL;
> -}
> -
> static inline bool sk_under_memory_pressure(const struct sock *sk)
> {
> if (!sk->sk_prot->memory_pressure)
> diff --git a/net/core/sock.c b/net/core/sock.c
> index 5440e67bcfe3..8d215f821ea6 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -3017,13 +3017,14 @@ int __sk_mem_raise_allocated(struct sock *sk, int size, int amt, int kind)
> }
> }
>
> - if (sk_has_memory_pressure(sk)) {
> - u64 alloc;
> -
> - if (!sk_under_memory_pressure(sk))
> - return 1;
> - alloc = sk_sockets_allocated_read_positive(sk);
> - if (sk_prot_mem_limits(sk, 2) > alloc *
> + if (prot->memory_pressure) {
> + /*
> + * If under global pressure, allow the sockets that are below
> + * average memory usage to raise, trying to be fair between all
> + * the sockets under global constrains.
> + */
> + if (!*prot->memory_pressure ||
> + sk_prot_mem_limits(sk, 2) > sk_sockets_allocated_read_positive(sk) *
The above introduces unrelated changes that makes the code IMHO less
readable - I don't see a good reason to drop the 'alloc' variable.
Cheers,
Paolo
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