Messages in this thread | | | Date | Fri, 01 Dec 2017 16:02:30 +0800 | From | Wei Wang <> | Subject | Re: [PATCH v18 05/10] xbitmap: add more operations |
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On 11/30/2017 06:34 PM, Tetsuo Handa wrote: > Wei Wang wrote: >> + * @start: the start of the bit range, inclusive >> + * @end: the end of the bit range, inclusive >> + * >> + * This function is used to clear a bit in the xbitmap. If all the bits of the >> + * bitmap are 0, the bitmap will be freed. >> + */ >> +void xb_clear_bit_range(struct xb *xb, unsigned long start, unsigned long end) >> +{ >> + struct radix_tree_root *root = &xb->xbrt; >> + struct radix_tree_node *node; >> + void **slot; >> + struct ida_bitmap *bitmap; >> + unsigned int nbits; >> + >> + for (; start < end; start = (start | (IDA_BITMAP_BITS - 1)) + 1) { >> + unsigned long index = start / IDA_BITMAP_BITS; >> + unsigned long bit = start % IDA_BITMAP_BITS; >> + >> + bitmap = __radix_tree_lookup(root, index, &node, &slot); >> + if (radix_tree_exception(bitmap)) { >> + unsigned long ebit = bit + 2; >> + unsigned long tmp = (unsigned long)bitmap; >> + >> + nbits = min(end - start + 1, BITS_PER_LONG - ebit); > "nbits = min(end - start + 1," seems to expect that start == end is legal > for clearing only 1 bit. But this function is no-op if start == end. > Please clarify what "inclusive" intended.
If xb_clear_bit_range(xb,10,10), then it is effectively the same as xb_clear_bit(10). Why would it be illegal?
"@start inclusive" means that the @start will also be included to be cleared.
> >> +static inline __always_inline void bitmap_clear(unsigned long *map, >> + unsigned int start, >> + unsigned int nbits) >> +{ >> + if (__builtin_constant_p(nbits) && nbits == 1) >> + __clear_bit(start, map); >> + else if (__builtin_constant_p(start & 7) && IS_ALIGNED(start, 8) && >> + __builtin_constant_p(nbits & 7) && IS_ALIGNED(nbits, 8)) > It looks strange to apply __builtin_constant_p test to variables after "& 7". >
I think this is normal - if the variables are known at compile time, the calculation will be done at compile time (termed constant folding).
Best, Wei
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