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SubjectRe: [PATCH] lib: bitmap: introduce bitmap_find_next_zero_area_and_size
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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@samsung.com>

The code itself is good, so

Acked-by: Michal Nazarewicz <mina86@mina86.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»

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