Re: 2.6.8.1-mm2

[Andrew Morton <akpm@osdl.org>]

Hans Reiser <reiser@namesys.com> wrote:
>
> John Cherry wrote:
> 
> >The new "errors" are from reiser4 code and they all appear to be...
> >
> >fs/reiser4/reiser4.h:18:2: #error "Please turn 4k stack off"
> >
> >  
> >
> zam, can you or Mr. Demidov work on using kmalloc to reduce stack usage?
> 
> Andrew suggested that for statically sized objects kmalloc is quite fast 
> (one instruction I think he said), so my objection to kmallocing a lot 
> has faded.

err, not that quick - but it's pretty quick.

With a kmalloc with a constant size and, preferably, a constant gfp mask
we'll jump directly into __cache_alloc() and in the common case we'll pluck
an entry directly out of the cpu-local head array:

So the kmalloc fastpath is, effectively:

	local_irq_save(save_flags);
	ac = ac_data(cachep);
	if (likely(ac->avail)) {
		ac->touched = 1;
		objp = ac_entry(ac)[--ac->avail];
	}
	local_irq_restore(save_flags);
	return objp;


Not bad...