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From: Vernon Mauery <vernux@us.ibm.com>
To: kernel list <linux-kernel@vger.kernel.org>
Subject: Re: kfree(NULL)
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On Friday 21 April 2006 12:22, you wrote:
> On Fri, Apr 21, 2006 at 05:07:45PM +0200, Jan Engelhardt wrote:
> > >> Maybe kfree should really be a wrapper around __kfree which does the
> > >> real work.  Then kfree could be a inlined function or a #define that
> > >> does the NULL pointer check.
> > >
> > >NULL pointer check in kfree saves lot of small code fragments in
> > > callers. It is one of many reasons why kfree does it.
> > >Making kfree inline wrapper eliminates this save.
> >
> > How about
> >
> > slab.h:
> > #ifndef CONFIG_OPTIMIZING_FOR_SIZE
> > static inline void kfree(const void *p) {
> >     if(p != NULL)
> >         __kfree(p);
> > }
> > #else
> > extern void kfree(const void *);
> > #endif
> >
> > slab.c:
> > #ifdef CONFIG_OPTIMIZING_FOR_SIZE
> > void kfree(const void *p) {
> >     if(p != NUILL)
> >         _kfree(p);
> > }
> > #endif
> >
> > That way, you get your time saving with -O2 and your space saving with
> > -Os.
>
> What makes you confident that the static inline version gives a time
> saving?

A static inline wrapper would mean that it wouldn't have to make a function 
call just to check if the pointer is NULL.  A simple NULL check is faster 
than a function call and then a simple NULL check.  In other words, there 
would be no pushing and popping the stack.  In almost all cases, replacing an 
inline function with a non-inline function means a trade-off between speed 
and size.

--Vernon