2012/5/23 Jan Kara <jack@xxxxxxx>:
> On Sun 20-05-12 22:23:14, Akinobu Mita wrote:
>> memweight() is the function that counts the total number of bits set
>> in memory area. The memory area doesn't need to be aligned to
>> long-word boundary unlike bitmap_weight().
> Thanks for the patch. I have some comments below.
Thanks for the review.
>> @@ -824,3 +825,39 @@ void *memchr_inv(const void *start, int c, size_t bytes)
>> return check_bytes8(start, value, bytes % 8);
>> }
>> EXPORT_SYMBOL(memchr_inv);
>> +
>> +/**
>> + * memweight - count the total number of bits set in memory area
>> + * @ptr: pointer to the start of the area
>> + * @bytes: the size of the area
>> + */
>> +size_t memweight(const void *ptr, size_t bytes)
>> +{
>> + size_t w = 0;
>> + size_t longs;
>> + union {
>> + const void *ptr;
>> + const unsigned char *b;
>> + unsigned long address;
>> + } bitmap;
> Ugh, this is ugly and mostly unnecessary. Just use "const unsigned char
> *bitmap".
>
>> +
>> + for (bitmap.ptr = ptr; bytes > 0 && bitmap.address % sizeof(long);
>> + bytes--, bitmap.address++)
>> + w += hweight8(*bitmap.b);
> This can be:
> count = ((unsigned long)bitmap) % sizeof(long);
The count should be the size of unaligned area and it can be greater than
bytes. So
count = min(bytes,
sizeof(long) - ((unsigned long)bitmap) % sizeof(long));
> while (count--) {
> w += hweight(*bitmap);
> bitmap++;
> bytes--;
> }
>> +
>> + for (longs = bytes / sizeof(long); longs > 0; ) {
>> + size_t bits = min_t(size_t, INT_MAX & ~(BITS_PER_LONG - 1),
>> + longs * BITS_PER_LONG);
> I find it highly unlikely that someone would have such a large bitmap
> (256 MB or more on 32-bit). Also the condition as you wrote it can just
> overflow so it won't have the desired effect. Just do
> BUG_ON(longs >= ULONG_MAX / BITS_PER_LONG);
The bits argument of bitmap_weight() is int type. So this should be
BUG_ON(longs >= INT_MAX / BITS_PER_LONG);
> and remove the loop completely. If someone comes with such a huge bitmap,
> the code can be modified easily (after really closely inspecting whether
> such a huge bitmap is really well justified).
size_t memweight(const void *ptr, size_t bytes)
{
size_t w = 0;
size_t longs;
const unsigned char *bitmap = ptr;
for (; bytes > 0 && ((unsigned long)bitmap) % sizeof(long);
bytes--, bitmap++)
w += hweight8(*bitmap);
longs = bytes / sizeof(long);
BUG_ON(longs >= INT_MAX / BITS_PER_LONG);
w += bitmap_weight((unsigned long *)bitmap, longs * BITS_PER_LONG);
bytes -= longs * sizeof(long);
bitmap += longs * sizeof(long);
for (; bytes > 0; bytes--, bitmap++)
w += hweight8(*bitmap);
return w;
}
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