Re: [patch] hugetlb: override default huge page size non-const fix

[Jon Tollefson <kniht@us.ibm.com>]

Nick Piggin wrote:
> Hi,
>
> I revisited the multi-size hugetlb patches, and realised I forgot one small
> outstanding issue. Your
> hugetlb-override-default-huge-page-size-ia64-build.patch
> fix basically disallows overriding of the default hugetlb size, because we
> always set the default back to HPAGE_SIZE.
>
> A better fix I think is just to initialize the default_hstate_size to an
> invalid value, which the init code checks for and reverts to HPAGE_SIZE
> anyway. So please replace that patch with this one.
>
> Overriding of the default hugepage size is not of major importance, but it
> can allow legacy code (providing it is well written), including the hugetlb
> regression suite to be run with different hugepage sizes (so actually it is
> quite important for developers at least).
>
> I don't have access to such a machine, but I hope (with this patch), the
> powerpc developers can run the libhugetlb regression suite one last time
> against a range of page sizes and ensure the results look reasonable.
>   
I am a little slow here, but I was able to boot with 
default_hugepagesz=64K and 16G on Power and it set the default huge page 
size to the given size.

Jon

> Thanks,
> Nick
>
> --
>
> If HPAGE_SIZE is not constant (eg. on ia64), then the initialiser does not
> work. Fix this by making default_hstate_size == 0, then if it isn't set
> from the cmdline, hugetlb_init will still do the right thing and set up the
> default hstate as (the now initialized) HPAGE_SIZE.
>
> Signed-off-by: Nick Piggin <npiggin@suse.de>
> ---
> Index: linux-2.6/mm/hugetlb.c
> ===================================================================
> --- linux-2.6.orig/mm/hugetlb.c
> +++ linux-2.6/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 = 0;
>
>  #define for_each_hstate(h) \
>  	for ((h) = hstates; (h) < &hstates[max_hstate]; (h)++)
>   

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