Messages in this thread | | | Date | Fri, 21 Apr 2006 23:38:46 +0200 | From | Adrian Bunk <> | Subject | Re: kfree(NULL) |
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On Fri, Apr 21, 2006 at 01:30:30PM -0700, Vernon Mauery wrote: > 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.
It's not that simple - inline's make the code bigger causing more cache misses and therefore also having a negative impact on performance.
This is the reason why e.g. the gcc -O3 option usually results in _worse_ performance than the -O2 option.
> --Vernon
cu Adrian
BTW: Don't strip the Cc when replying to linux-kernel.
--
"Is there not promise of rain?" Ling Tan asked suddenly out of the darkness. There had been need of rain for many days. "Only a promise," Lao Er said. Pearl S. Buck - Dragon Seed
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