linux-kernel - Re: Problem in pfmemalloc skb handling in net/core/dev.c

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Date:   Fri, 9 Apr 2021 03:08:17 -0700
From:   Xie He <xie.he.0141@...il.com>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     Mel Gorman <mgorman@...e.de>, jslaby@...e.cz,
        Neil Brown <neilb@...e.de>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Mike Christie <michaelc@...wisc.edu>,
        Eric B Munson <emunson@...bm.net>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Sebastian Andrzej Siewior <sebastian@...akpoint.cc>,
        Christoph Lameter <cl@...ux.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: Problem in pfmemalloc skb handling in net/core/dev.c

On Fri, Apr 9, 2021 at 2:58 AM Mel Gorman <mgorman@...hsingularity.net> wrote:
>
> On Fri, Apr 09, 2021 at 02:14:12AM -0700, Xie He wrote:
> >
> > Do you mean that at the time "sk_memalloc_socks()" changes from "true"
> > to "false", there would be no in-flight skbs currently being received,
> > and all network communications have been paused?
>
> Not all network communication, but communication with swap devices
> should have stopped once sk_memalloc_socks is false.

But all incoming network traffic can be allocated as pfmemalloc skbs,
regardless whether or not it is related to swap devices. My protocols
don't need and cannot handle pfmemalloc skbs, therefore I want to make
sure my protocols never receive pfmemalloc skbs. The current code
doesn't seem to guarantee this.