Re: [patch 15/21] hugetlb: override default huge page size

[Nick Piggin <npiggin@suse.de>]

On Mon, Jun 09, 2008 at 03:41:26AM -0700, Andrew Morton wrote:
> On Wed, 04 Jun 2008 21:29:54 +1000 npiggin@suse.de wrote:
> 
> > Allow configurations with the default huge page size which is different to
> > the traditional HPAGE_SIZE size. The default huge page size is the one
> > represented in the legacy /proc ABIs, SHM, and which is defaulted to when
> > mounting hugetlbfs filesystems.
> > 
> > This is implemented with a new kernel option default_hugepagesz=, which
> > defaults to HPAGE_SIZE if not specified.
> > 
> > ...
> >
> > --- linux-2.6.orig/mm/hugetlb.c	2008-06-04 20:51:23.000000000 +1000
> > +++ linux-2.6/mm/hugetlb.c	2008-06-04 20:51:24.000000000 +1000
> > @@ -34,6 +34,7 @@ struct hstate hstates[HUGE_MAX_HSTATE];
> >  /* for command line parsing */
> >  static struct hstate * __initdata parsed_hstate = NULL;
> >  static unsigned long __initdata default_hstate_max_huge_pages = 0;
> > +static unsigned long __initdata default_hstate_size = HPAGE_SIZE;
> 
> ia64:
> 
> mm/hugetlb.c:39: error: initializer element is not constant
> 
> (wtf?)

Oh, hmm, despite attempts to hide it behind macros, HPAGE_SHIFT seems
like it is boot time configurable.


> Hopefully this'll fix it.

It will be fine for the time being, thanks. It actually will break the
default hstate size selection (because the parameter parsing code runs
first and might want to override default_hstate_size). But don't worry
about that, I'll see if I can find a solution for ia64.

Ideally, ia64 will convert HPAGE_SHIFT to their constant HPAGE_SHIFT_DEFAULT,
and then implement the new size selection API that this patchset introduces.

But for now, yes, fine, thanks.

> 
> --- a/mm/hugetlb.c~hugetlb-override-default-huge-page-size-ia64-build
> +++ a/mm/hugetlb.c
> @@ -34,7 +34,7 @@ struct hstate hstates[HUGE_MAX_HSTATE];
>  /* for command line parsing */
>  static struct hstate * __initdata parsed_hstate;
>  static unsigned long __initdata default_hstate_max_huge_pages;
> -static unsigned long __initdata default_hstate_size = HPAGE_SIZE;
> +static unsigned long __initdata default_hstate_size;
>  
>  #define for_each_hstate(h) \
>  	for ((h) = hstates; (h) < &hstates[max_hstate]; (h)++)
> @@ -1208,6 +1208,8 @@ static int __init hugetlb_init(void)
>  {
>  	BUILD_BUG_ON(HPAGE_SHIFT == 0);
>  
> +	default_hstate_size = HPAGE_SIZE;
> +
>  	if (!size_to_hstate(default_hstate_size)) {
>  		default_hstate_size = HPAGE_SIZE;
>  		if (!size_to_hstate(default_hstate_size))
> _

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