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

From: Jay Lan
Date: Thu Aug 03 2006 - 17:13:18 EST

Andrew Morton wrote:
On Wed, 02 Aug 2006 21:23:35 -0700
Jay Lan <jlan@xxxxxxxxxxxx> 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?


We export to userspace the acct_rss_mem1 and acct_vm_mem1, both as u64.
The above logic is to calculate stime delta since last update. Note that
acc_update_integrals() is invoked at do_execve, do_exit, _AND_ at
account_system_time, which is called every jiffy by timer interrupt

The tsk->acct_stimexpd is used to save the tsk->stime of last update.
It should be changed to cputime_t as well. I will include the fix in
my next fix patch.

+ 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

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 ;)

This is not a BSD accounting thing. It came from UNICOS and IRIX.
I am pinging the person who knows how the real world users use these
two fields...

- jay

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