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[space-map-disk] improve performance of finding a free bitmap entry

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* Simply test the raw bitmap entries against zero, to avoid
  time-consumed reference-count value extraction.

* Improve the way of iterating entries inside a bitmap:
  Extract 64-bit of bitmap entries at once, and use bitwise shift
  to iterate through the entries.
This commit is contained in:
Ming-Hung Tsai 2018-10-31 18:10:51 +08:00
parent cb0a77e2ae
commit 7a1c6dc4bf
1 changed files with 32 additions and 3 deletions
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35
persistent-data/space-maps/disk.cc
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@ -153,11 +153,27 @@ namespace {
}
boost::optional<unsigned> find_free(unsigned begin, unsigned end) {
begin = max(begin, ie_.none_free_before_);
if (begin >= end)
return boost::optional<unsigned>();
read_ref rr = tm_.read_lock(ie_.blocknr_, validator_);
void const *bits = bitmap_data(rr);
for (unsigned i = max(begin, ie_.none_free_before_); i < end; i++)
if (__lookup_raw(bits, i) == 0)
return boost::optional<unsigned>(i);
// specify the search range inside the bitmap, in 64-bit unit
le64 const *w = reinterpret_cast<le64 const *>(bits);
le64 const *le64_begin = w + (begin >> 5); // w + div_down(begin, 32)
le64 const *le64_end = w + ((end + 31) >> 5); // w + div_up(end, 32)
for (le64 const *ptr = le64_begin; ptr < le64_end; ptr++) {
// specify the search range among a 64-bit of entries
unsigned entry_begin = (ptr == le64_begin) ? (begin & 0x1F) : 0;
unsigned entry_end = ((ptr == le64_end - 1) && (end & 0x1F)) ?
(end & 0x1F) : 32;
int i;
if ((i = find_free_entry(ptr, entry_begin, entry_end)) >= 0)
return ((ptr - w) << 5) + i;
}
return boost::optional<unsigned>();
}
@ -198,6 +214,19 @@ namespace {
return result;
}
// find a free entry (a 2-bit pair) among the specified range in the input bits
int find_free_entry(le64 const* bits, unsigned entry_begin, unsigned entry_end) {
uint64_t v = to_cpu<uint64_t>(*bits);
v >>= (entry_begin * 2);
for (; entry_begin < entry_end; entry_begin++) {
if (!(v & 0x3)) {
return entry_begin;
}
v = v >> 2;
}
return -1;
}
transaction_manager &tm_;
bcache::validator::ptr validator_;