Re: [patch 2/2] mm: use vm_unmapped_area() on powerpc architecture

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>]

akpm@linux-foundation.org writes:

> From: Michel Lespinasse <walken@google.com>
> Subject: mm: use vm_unmapped_area() on powerpc architecture
>
> Update the powerpc slice_get_unmapped_area function to make use of
> vm_unmapped_area() instead of implementing a brute force search.
>
> Signed-off-by: Michel Lespinasse <walken@google.com>
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Cc: Paul Mackerras <paulus@samba.org>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
>
>  arch/powerpc/mm/slice.c |  123 ++++++++++++++++++++++++--------------
>  1 file changed, 78 insertions(+), 45 deletions(-)
>
> diff -puN arch/powerpc/mm/slice.c~mm-use-vm_unmapped_area-on-powerpc-architecture arch/powerpc/mm/slice.c
> --- a/arch/powerpc/mm/slice.c~mm-use-vm_unmapped_area-on-powerpc-architecture
> +++ a/arch/powerpc/mm/slice.c
> @@ -237,36 +237,69 @@ static void slice_convert(struct mm_stru
>  #endif
>  }
>
> +/*
> + * Compute which slice addr is part of;
> + * set *boundary_addr to the start or end boundary of that slice
> + * (depending on 'end' parameter);
> + * return boolean indicating if the slice is marked as available in the
> + * 'available' slice_mark.
> + */
> +static bool slice_scan_available(unsigned long addr,
> +				 struct slice_mask available,
> +				 int end,
> +				 unsigned long *boundary_addr)
> +{
> +	unsigned long slice;
> +	if (addr < SLICE_LOW_TOP) {
> +		slice = GET_LOW_SLICE_INDEX(addr);
> +		*boundary_addr = (slice + end) << SLICE_LOW_SHIFT;
> +		return !!(available.low_slices & (1u << slice));
> +	} else {
> +		slice = GET_HIGH_SLICE_INDEX(addr);
> +		*boundary_addr = (slice + end) ?
> +			((slice + end) << SLICE_HIGH_SHIFT) : SLICE_LOW_TOP;
> +		return !!(available.high_slices & (1u << slice));
> +	}
> +}


Can you clarify more on when boundary_addr is set to start of the slice
in the comment ? Also may be it would be better if we can say
slice_scan_prev_available and slice_scan_next_available and get rid of
end completely ?

I have tested with both the patches applied and the resulting kernel boots fine. 

-aneesh