netdev - Re: [PATCH net-next] tcp: forbid direct reclaim if MSG

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Date:   Wed, 10 Oct 2018 09:30:44 +0800
From:   Yafang Shao <laoar.shao@...il.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next] tcp: forbid direct reclaim if MSG_DONTWAIT is
 set in send path

On Tue, Oct 9, 2018 at 11:38 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
> On Tue, Oct 9, 2018 at 7:58 AM Eric Dumazet <edumazet@...gle.com> wrote:
> >
>
> > We do not add bloat in the kernel if no application is ever going to
> > use it, especially in the TCP fast path.
> >
>
> BTW, are you willing to change all memory allocations in the kernel as well ?
>
> Let say an application is using a system call providing a pathname
> (open(), stat(), ...), how this system call
> is going to ask the kernel for no direct reclaim ?
>
> Even allocating a socket with socket() or accept() has no ability to
> avoid direct reclaim.
>
> So tcp_sendmsg() is only the tip of the iceberg.

If we can really find a solution that is good enough to hanlde direct
reclaim in tcp_sendmsg,
we could also implement it in other syscalls.
Unexpected latency is hateful.

Thanks
Yafang