Re: [RFC][PATCH] inline a few tiny functions in init/initramfs.c

[Nick Piggin <nickpiggin@yahoo.com.au>]

Con Kolivas wrote:

> On Sat, 24 Sep 2005 09:26, Jesper Juhl wrote:
>
> > A few functions in init/initramfs.c are so simple that I don't see why
> > *any* point in them having to bear the cost of a function call.
> > Wouldn't something like the patch below make sense ?
>
> > -static void __init *malloc(size_t size)
> > +static inline void __init *malloc(size_t size)
> > {
> > 	return kmalloc(size, GFP_KERNEL);
>
> maybe it looks like it would, but kmalloc looks like this:
>
> 85 static inline void *kmalloc(size_t size, int flags)
> 86 {
> 87         if (__builtin_constant_p(size)) {
> 88                 int i = 0;
> 89 #define CACHE(x) \
> 90                 if (size <= x) \
> 91                         goto found; \
> 92                 else \
> 93                         i++;
> 94 #include "kmalloc_sizes.h"
> 95 #undef CACHE
> 96                 {
> 97                         extern void __you_cannot_kmalloc_that_much(void);
> 98                         __you_cannot_kmalloc_that_much();
> 99                 }
> 100 found:
> 101                 return kmem_cache_alloc((flags & GFP_DMA) ?
> 102                         malloc_sizes[i].cs_dmacachep :
> 103                         malloc_sizes[i].cs_cachep, flags);
> 104         }
> 105         return __kmalloc(size, flags);
> 106 }
>
> which is not a one liner to inline at all

Actually, this is even better, because the inline 'malloc' should be
able to propogate the builtin_constantness of 'size' while an out of
line version cannot.

IMO the best policy is not to second guess the API implementor's
choice of inline / noinline. That is - if kmalloc was too big to
inline then it should be fixed in kmalloc or another interface
introduced.

Nick


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