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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Tue, 24 Aug 2021 16:26:59 -0700
Message-ID: <CAHk-=wg8XonsSN1SXjpSh3pO3-+EMZvdkb1xwJbLpZxCT2=thQ@mail.gmail.com>
Subject: Re: 5.14-rc breaks iotop swap io monitoring.
To:     Dave Jones <davej@codemonkey.org.uk>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Linux Kernel <linux-kernel@vger.kernel.org>,
        Johannes Weiner <hannes@cmpxchg.org>
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On Tue, Aug 24, 2021 at 2:41 PM Dave Jones <davej@codemonkey.org.uk> wrote:
>
> On Tue, Aug 24, 2021 at 09:34:02AM -0700, Linus Torvalds wrote:
>  >
>  > What happens if you boot with the 'delayacct' kernel parameter.
>  >
>  > Even if you enable it at run-time, processes that have been started
>  > before it was enabled won't actually have the 'tsk->delays'
>  > allocation. So I'm not sure how effective the run-time thing is.
>
> Yeah that boot option does make iotop work again.

Ok, so it's that delay allocation thing is it.

I'm inclined to let it be and see if somebody else notices, and how
big of a deal it is.

The 'delayacct' kernel command line is an acceptable workaround if
this is something only a few people will even notice or care about.

I wonder how much people care about some statistics and iotop these days.

I also assume the swap stats still show up in "vmstat" etc, and that
it's just that iotop ended up using fancier interfaces?

Or do I assume wrongly?

           Linus