linux-kernel - Re: [PATCH v4 1/5] powerpc/mm/slice: Remove intermediate bitmap copy

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Date:   Sun, 11 Feb 2018 00:43:09 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     Christophe Leroy <christophe.leroy@....fr>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Scott Wood <oss@...error.net>, aneesh.kumar@...ux.vnet.ibm.com,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v4 1/5] powerpc/mm/slice: Remove intermediate bitmap
 copy

On Sat, 10 Feb 2018 13:54:25 +0100 (CET)
Christophe Leroy <christophe.leroy@....fr> wrote:

> bitmap_or() and bitmap_andnot() can work properly with dst identical
> to src1 or src2. There is no need of an intermediate result bitmap
> that is copied back to dst in a second step.

Everyone seems to be working on the slice code all of a sudden. I
had the same change in my series I just posted, but I didn't notice
this one of yours earlier, and it's better split out, so this is
fine by me.

Reviewed-by: Nicholas Piggin <npiggin@...il.com>

> 
> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
> Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
> ---
>  v2: New in v2
>  v3: patch moved up front of the serie to avoid ephemeral slice_bitmap_copy() function in following patch
>  v4: No change
> 
>  arch/powerpc/mm/slice.c | 12 ++++--------
>  1 file changed, 4 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/powerpc/mm/slice.c b/arch/powerpc/mm/slice.c
> index 23ec2c5e3b78..98b53d48968f 100644
> --- a/arch/powerpc/mm/slice.c
> +++ b/arch/powerpc/mm/slice.c
> @@ -388,21 +388,17 @@ static unsigned long slice_find_area(struct mm_struct *mm, unsigned long len,
>  
>  static inline void slice_or_mask(struct slice_mask *dst, struct slice_mask *src)
>  {
> -	DECLARE_BITMAP(result, SLICE_NUM_HIGH);
> -
>  	dst->low_slices |= src->low_slices;
> -	bitmap_or(result, dst->high_slices, src->high_slices, SLICE_NUM_HIGH);
> -	bitmap_copy(dst->high_slices, result, SLICE_NUM_HIGH);
> +	bitmap_or(dst->high_slices, dst->high_slices, src->high_slices,
> +		  SLICE_NUM_HIGH);
>  }
>  
>  static inline void slice_andnot_mask(struct slice_mask *dst, struct slice_mask *src)
>  {
> -	DECLARE_BITMAP(result, SLICE_NUM_HIGH);
> -
>  	dst->low_slices &= ~src->low_slices;
>  
> -	bitmap_andnot(result, dst->high_slices, src->high_slices, SLICE_NUM_HIGH);
> -	bitmap_copy(dst->high_slices, result, SLICE_NUM_HIGH);
> +	bitmap_andnot(dst->high_slices, dst->high_slices, src->high_slices,
> +		      SLICE_NUM_HIGH);
>  }
>  
>  #ifdef CONFIG_PPC_64K_PAGES