linux-kernel - Re: [patch 3/3] convert CONFIG tag for extended accounting routines

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Message-Id: <20060803000331.22fcb4c0.akpm@osdl.org>
Date:	Thu, 3 Aug 2006 00:03:31 -0700
From:	Andrew Morton <akpm@...l.org>
To:	Jay Lan <jlan@...r.sgi.com>
Cc:	linux-kernel@...r.kernel.org, nagar@...son.ibm.com,
	balbir@...ibm.com, jes@....com, csturtiv@....com, tee@....com,
	guillaume.thouvenin@...l.net
Subject: Re: [patch 3/3] convert CONFIG tag for extended accounting routines

On Wed, 02 Aug 2006 21:23:35 -0700
Jay Lan <jlan@...r.sgi.com> wrote:

> +/**
> + * acct_update_integrals - update mm integral fields in task_struct
> + * @tsk: task_struct for accounting
> + */
> +void acct_update_integrals(struct task_struct *tsk)
> +{
> +	if (likely(tsk->mm)) {
> +		long delta =
> +			cputime_to_jiffies(tsk->stime) - tsk->acct_stimexpd;

If a 32 architecture chooses to implement a 64-bit cputime_t, this
expression might go wrong for very long-running tasks and high HZ.

Perhaps we should do all this in terms of cputime_t and export everything
to userspace as u64?

> +		if (delta == 0)
> +			return;
> +		tsk->acct_stimexpd = tsk->stime;
> +		tsk->acct_rss_mem1 += delta * get_mm_rss(tsk->mm);
> +		tsk->acct_vm_mem1 += delta * tsk->mm->total_vm;

It's a bit weird to be multiplying RSS by time.  What unit is a "byte
second"?

If this is not a bug then I guess this is an intermediate term for
additional downstream processing.  There is information loss here and I'd
have thought that it would be better to simply send `delta' and the rss
straight to userspace, let userspace work out what math it wants to perform
on it.  If that makes sense?

I see that the code has been like this for a long time, so treat this as a
"please educate me about BSD accounting" email ;)

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