Messages in this thread Patch in this message | ![/](/images/icornerl.gif) | | Date | Thu, 27 Apr 2006 13:41:03 +0200 | From | Bart Hartgers <> | Subject | Re: [PATCH] likely cleanup: remove unlikely for kfree(NULL) |
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Arjan van de Ven wrote: > On Thu, 2006-04-27 at 10:56 +0200, Adrian Bunk wrote: >> On Thu, Apr 27, 2006 at 10:41:12AM +0200, Arjan van de Ven wrote: >>> On Thu, 2006-04-27 at 10:31 +0200, Adrian Bunk wrote: >>>> On Thu, Apr 27, 2006 at 08:50:40AM +0200, Arjan van de Ven wrote: >>>>> On Thu, 2006-04-27 at 09:28 +0300, Pekka J Enberg wrote: >>>>>> On Thu, 27 Apr 2006, Nick Piggin wrote: >>>>>>> Not to dispute your conclusions or method, but I think doing a >>>>>>> defconfig or your personal config might be more representative >>>>>>> of % size increase of text that will actually be executed. And >>>>>>> that is the expensive type of text. >>>>>> True but I was under the impression that Arjan thought we'd get text >>>>>> savings with GCC 4.1 by making kfree() inline. >>>>> not savings in text size, I'll settle for the same size. >>>>> ... >>>> It will always be bigger since there are cases where it's unknown at >>>> compile time whether it will be NULL when called. >>> if it's "unknown" you could call into a separate kfree() which does >>> check out of line. (sure that's a dozen bytes bigger but that is >>> noise ;) >> It's noise and _much work. > > not if the compiler can do it. The *compiler* knows a lot (4.1 at > least)..
I would think so too. Unfortunately this is what I found for make allyesconfig on 2.6.16.9:
text data bss dec hex filename 21615935 7929490 2187672 31733097 1e43569 vmlinux-3.3.5-new 21616824 7929298 2187672 31733794 1e43822 vmlinux-3.3.5-old 21546713 7616546 2184984 31348243 1de5613 vmlinux-4.1.0-new 21546551 7616458 2184984 31347993 1de5519 vmlinux-4.1.0-old
Where "old" is the original one, and "new" the one with the included patch applied. So the patch is a small win with gcc-3.3.5 and a small loss on gcc-4.1.0. I don't really understand why 4.1.0 produces larger code with the patch, but I triple-checked...
Groeten, Bart
-- Bart Hartgers - TUE Eindhoven - http://plasimo.phys.tue.nl/bart/contact/ --- linux-2.6.16.9/include/linux/slab.h 2006-04-19 08:10:14.000000000 +0200 +++ linux-2.6.16.9-kfree/include/linux/slab.h 2006-04-27 11:19:00.000000000 +0200 @@ -123,7 +123,18 @@ return kzalloc(n * size, flags); } -extern void kfree(const void *); +extern void __kfree(const void *); + +static inline void kfree(const void *ptr) +{ + if (__builtin_constant_p(ptr==NULL)) { + if (ptr) + __kfree(ptr); + } else { + __kfree(ptr); + } +} + extern unsigned int ksize(const void *); #ifdef CONFIG_NUMA --- linux-2.6.16.9/mm/slab.c 2006-04-27 11:24:38.000000000 +0200 +++ linux-2.6.16.9-kfree/mm/slab.c 2006-04-27 11:17:06.000000000 +0200 @@ -3267,7 +3267,7 @@ EXPORT_SYMBOL(kmem_cache_free); /** - * kfree - free previously allocated memory + * __kfree - free previously allocated memory * @objp: pointer returned by kmalloc. * * If @objp is NULL, no operation is performed. @@ -3275,7 +3275,7 @@ * Don't free memory not originally allocated by kmalloc() * or you will run into trouble. */ -void kfree(const void *objp) +void __kfree(const void *objp) { struct kmem_cache *c; unsigned long flags; | ![\](/images/icornerr.gif) |