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

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Date:   Sat, 10 Feb 2018 15:57:25 +0100
From:   Christophe LEROY <christophe.leroy@....fr>
To:     Nicholas Piggin <npiggin@...il.com>
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



Le 10/02/2018 à 15:43, Nicholas Piggin a écrit :
> 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.

Thanks,

I had a quick look at your serie, it looks promising.

The main purpose of mine is to allow the use of slies on the 8xx in 
order to fix a hugepage related bug.

Your serie is performance oriented and seems nice, indeed I should have 
noticed that it was passing huge structures instead of pointers to 
subfunctions. I will look at your serie more in details next week.

Christophe


> 
> 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