Re: kfree(NULL)

[Tilman Schmidt]

On 21.04.2006 11:00, Andrew Morton wrote:

> James Morris <jmorris@xxxxxxxxx> wrote:
> 
>>On Fri, 21 Apr 2006, Daniel Walker wrote:
>>
>>>	I included a patch , not like it's needed . Recently I've been
>>>evaluating likely/unlikely branch prediction .. One thing that I found 
>>>is that the kfree function is often called with a NULL "objp" . In fact
>>>it's so frequent that the "unlikely" branch predictor should be inverted!
>>>Or at least on my configuration. 
>>
>>It would be helpful to collect some stats on this so we can look at the 
>>ratio.
> 
> Yes, kfree(NULL) is supposed to be uncommon.

Not anymore, after the recent campaign to elliminate explicit NULL
checks before calls to kfree().

> If someone's doing it a lot then we should fix up the callers.

If that fixup amounts to re-adding the NULL check just elliminated
then that's no improvement. It would be better to drop the assumption
that kfree() calls with a NULL argument are uncommon, and consequently
remove the unlikely() predictor. Adding likely() instead may or may
not be a good idea.

-- 
Tilman Schmidt                          E-Mail: tilman@xxxxxxx
Bonn, Germany
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