netdev - RE: [PATCH net 1/1] net: tcp: Don't increase the TCP_MIB

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Date:   Thu, 6 Apr 2017 22:05:43 +0800
From:   "Gao Feng" <gfree.wind@...mail.com>
To:     "'Neal Cardwell'" <ncardwell@...gle.com>,
        "'Gao Feng'" <gfree.wind@...mail.com>
Cc:     "'David Miller'" <davem@...emloft.net>,
        "'Alexey Kuznetsov'" <kuznet@....inr.ac.ru>,
        "'James Morris'" <jmorris@...ei.org>,
        "'Patrick McHardy'" <kaber@...sh.net>,
        "'Netdev'" <netdev@...r.kernel.org>
Subject: RE: [PATCH net 1/1] net: tcp: Don't increase the TCP_MIB_OUTRSTS when fail to transmit RST

Hi Neal,

> -----Original Message-----
> From: Neal Cardwell [mailto:ncardwell@...gle.com]
> Sent: Thursday, April 6, 2017 10:01 PM
> To: Gao Feng <gfree.wind@...mail.com>
> Cc: David Miller <davem@...emloft.net>; Alexey Kuznetsov
> <kuznet@....inr.ac.ru>; James Morris <jmorris@...ei.org>; Patrick McHardy
> <kaber@...sh.net>; Netdev <netdev@...r.kernel.org>; Gao Feng
> <fgao@...ai8.com>
> Subject: Re: [PATCH net 1/1] net: tcp: Don't increase the TCP_MIB_OUTRSTS
> when fail to transmit RST
> 
> On Thu, Apr 6, 2017 at 9:35 AM,  <gfree.wind@...mail.com> wrote:
> > From: Gao Feng <fgao@...ai8.com>
> >
> > When fail to transmit RST, don't increase TCP_MIB_OUTRSTS in func
> > tcp_send_active_reset like the case that it only increases
> > LINUX_MIB_TCPABORTFAILED when fail to alloc skb.
> >
> > Signed-off-by: Gao Feng <fgao@...ai8.com>
> > ---
> 
> I would be concerned that this is a change in the semantics of
> TCP_MIB_OUTRSTS that might break user-space monitoring tools that rely on
> the current semantics. Counting attempted RSTs could be an important signal
> to monitor, and it could be quite bad if that signal is lost or hidden because the
> machine is so overloaded that the transmission of the RSTs fails.
> 
> Also it would seem to muddy the semantics a bit, since both
> tcp_v4_send_reset() and tcp_v6_send_response() currently increment
> TCP_MIB_OUTRSTS without regard to whether the transmit actually succeeded
> or not.
> 
> neal
If so, we should increase the TCP_MIB_OUTRSTS too when fail to alloc skb.
When machine is overloaded and mem is exhausted, it may fail to alloc skb.

Regards
Feng