Re: [PATCH net-next] tcp: forbid direct reclaim if MSG_DONTWAIT is set in send path

From: Yafang Shao
Date: Tue Oct 09 2018 - 21:31:24 EST

On Tue, Oct 9, 2018 at 11:38 PM Eric Dumazet <edumazet@xxxxxxxxxx> wrote:
> On Tue, Oct 9, 2018 at 7:58 AM Eric Dumazet <edumazet@xxxxxxxxxx> 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.