linux-kernel - Re: [PATCH] lib: bitmap: introduce bitmap_find_next_zero_area_and

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Date:   Wed, 28 Dec 2016 15:14:06 +0100
From:   Michal Nazarewicz <mina86@...a86.com>
To:     Jaewon Kim <jaewon31.kim@...sung.com>,
        Michal Hocko <mhocko@...nel.org>
Cc:     gregkh@...uxfoundation.org, akpm@...ux-foundation.org,
        labbott@...hat.com, m.szyprowski@...sung.com,
        gregory.0xf0@...il.com, laurent.pinchart@...asonboard.com,
        akinobu.mita@...il.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, jaewon31.kim@...il.com
Subject: Re: [PATCH] lib: bitmap: introduce bitmap_find_next_zero_area_and_size

On Wed, Dec 28 2016, Jaewon Kim wrote:
> I did not add caller in this patch.
> I am using the patch in cma_alloc function like below to show
> available page status.
>
> +               printk("number of available pages: ");
> +               start = 0;
> +               for (;;) {
> +                       bitmap_no = bitmap_find_next_zero_area_and_size(cma->bitmap,
> +                                               cma->count, start, &nr);
> +                       if (bitmap_no >= cma->count)
> +                               break;
> +                       if (nr_total == 0)
> +                               printk("%u", nr);
> +                       else
> +                               printk("+%u", nr);
> +                       nr_total += nr;
> +                       start = bitmap_no + nr;
> +               }
> +               printk("=>%u pages, total: %lu pages\n", nr_total, cma->count);

I would be happier should you find other existing places where this
function can be used.  With just one caller, I’m not convinced it is
worth it.

>>> Signed-off-by: Jaewon Kim <jaewon31.kim@...sung.com>

The code itself is good, so

Acked-by: Michal Nazarewicz <mina86@...a86.com>

and I’ll leave deciding whether it improves the kernel overall to
maintainers. ;)

>>> ---
>>>  include/linux/bitmap.h |  6 ++++++
>>>  lib/bitmap.c           | 25 +++++++++++++++++++++++++
>>>  2 files changed, 31 insertions(+)
>>>
>>> diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
>>> index 3b77588..b724a6c 100644
>>> --- a/include/linux/bitmap.h
>>> +++ b/include/linux/bitmap.h
>>> @@ -46,6 +46,7 @@
>>>   * bitmap_clear(dst, pos, nbits)		Clear specified bit area
>>>   * bitmap_find_next_zero_area(buf, len, pos, n, mask)	Find bit free area
>>>   * bitmap_find_next_zero_area_off(buf, len, pos, n, mask)	as above
>>> + * bitmap_find_next_zero_area_and_size(buf, len, pos, n, mask)	Find bit free area and its size
>>>   * bitmap_shift_right(dst, src, n, nbits)	*dst = *src >> n
>>>   * bitmap_shift_left(dst, src, n, nbits)	*dst = *src << n
>>>   * bitmap_remap(dst, src, old, new, nbits)	*dst = map(old, new)(src)
>>> @@ -123,6 +124,11 @@ extern unsigned long bitmap_find_next_zero_area_off(unsigned long *map,
>>>  						    unsigned long align_mask,
>>>  						    unsigned long align_offset);
>>>  
>>> +extern unsigned long bitmap_find_next_zero_area_and_size(unsigned long *map,
>>> +							 unsigned long size,
>>> +							 unsigned long start,
>>> +							 unsigned int *nr);
>>> +
>>>  /**
>>>   * bitmap_find_next_zero_area - find a contiguous aligned zero area
>>>   * @map: The address to base the search on
>>> diff --git a/lib/bitmap.c b/lib/bitmap.c
>>> index 0b66f0e..d02817c 100644
>>> --- a/lib/bitmap.c
>>> +++ b/lib/bitmap.c
>>> @@ -332,6 +332,31 @@ unsigned long bitmap_find_next_zero_area_off(unsigned long *map,
>>>  }
>>>  EXPORT_SYMBOL(bitmap_find_next_zero_area_off);
>>>  
>>> +/**
>>> + * bitmap_find_next_zero_area_and_size - find a contiguous aligned zero area
>>> + * @map: The address to base the search on
>>> + * @size: The bitmap size in bits
>>> + * @start: The bitnumber to start searching at
>>> + * @nr: The number of zeroed bits we've found
>>> + */
>>> +unsigned long bitmap_find_next_zero_area_and_size(unsigned long *map,
>>> +					     unsigned long size,
>>> +					     unsigned long start,
>>> +					     unsigned int *nr)
>>> +{
>>> +	unsigned long index, i;
>>> +
>>> +	*nr = 0;
>>> +	index = find_next_zero_bit(map, size, start);
>>> +
>>> +	if (index >= size)
>>> +		return index;

I would remove this check.  find_next_bit handles situation when index
== size and without this early return, *nr is always set.

>>> +	i = find_next_bit(map, size, index);
>>> +	*nr = i - index;
>>> +	return index;
>>> +}
>>> +EXPORT_SYMBOL(bitmap_find_next_zero_area_and_size);
>>> +
>>>  /*
>>>   * Bitmap printing & parsing functions: first version by Nadia Yvette Chambers,
>>>   * second version by Paul Jackson, third by Joe Korty.
>>> -- 
>>> 1.9.1
>>>
>>> --
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>

-- 
Best regards
ミハウ “𝓶𝓲𝓷𝓪86” ナザレヴイツ
«If at first you don’t succeed, give up skydiving»