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Date:   Mon, 9 Oct 2023 10:43:41 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     brookxu <brookxu.cn@gmail.com>
Cc:     bsingharora@gmail.com, juri.lelli@redhat.com,
        vincent.guittot@linaro.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/3] delayacct: convert task->delays to a object
Message-ID: <20231009084341.GA14330@noisy.programming.kicks-ass.net>
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On Sun, Oct 08, 2023 at 07:10:01PM +0800, brookxu wrote:

> > > @@ -1331,7 +1332,7 @@ struct task_struct {
> > >   	struct page_frag		task_frag;
> > >   #ifdef CONFIG_TASK_DELAY_ACCT
> > > -	struct task_delay_info		*delays;
> > > +	struct task_delay_info		delays;
> > >   #endif
> > Yeah, no.

> Yes, this way will increase about 80 bytes for task_struct, about 0.85% of
> size of task_struct, I think this just like sched_statistics, so that can
> better support dynamically enable through sysctl.

But it's 80 bytes 'nobody' will use. And arguably we should do the same
with schedstats, that's default disabled and again, that's per-task
storage nobody ever uses.

Per this argument we can grow task_struct indefinitely until it
collapses in on itself by the sheer weight of it's information density.
Every additional field will be a smaller fraction of the total.

Yes, it makes it all a little more cumbersome, but we should really not
burden everybody with the load of some.

Surely there is another solution... ?