osd: add pg_pool_t::get_pg_num_divisor

A PG is not always an equally sized fraction of the total pool size due to
the use of ceph_stable_mod.  Add a helper to return the fraction
(denominator) of a given pg based on the current pg_num value.

Signed-off-by: Sage Weil <sage@inktank.com>

diff --git a/src/osd/osd_types.cc b/src/osd/osd_types.cc
index 2e43c51abcb750b5559b57d9b295c4ab58becdb2..5018062e207a5b4c1fe204090734153f39f4cdf9 100644 (file)
--- a/src/osd/osd_types.cc
+++ b/src/osd/osd_types.cc
@@ -750,6 +750,17 @@ void pg_pool_t::calc_pg_masks()
   pgp_num_mask = (1 << calc_bits_of(pgp_num-1)) - 1;
 }
 
+unsigned pg_pool_t::get_pg_num_divisor(pg_t pgid) const
+{
+  if (pg_num == pg_num_mask + 1)
+    return pg_num;                    // power-of-2 split
+  unsigned mask = pg_num_mask >> 1;
+  if ((pgid.ps() & mask) < (pg_num & mask))
+    return pg_num_mask + 1;           // smaller bin size (already split)
+  else
+    return (pg_num_mask + 1) >> 1;    // bigger bin (not yet split)
+}
+
 /*
  * we have two snap modes:
  *  - pool global snaps

diff --git a/src/osd/osd_types.h b/src/osd/osd_types.h
index feabbd6e2ea5dad508a47ae72789bc681aa9bd5b..5db79572c9fe933f64ab466f6948862041ed7918 100644 (file)
--- a/src/osd/osd_types.h
+++ b/src/osd/osd_types.h
@@ -811,7 +811,7 @@ public:
    */
   interval_set<snapid_t> removed_snaps;
 
-  int pg_num_mask, pgp_num_mask;
+  unsigned pg_num_mask, pgp_num_mask;
 
   set<uint64_t> tiers;      ///< pools that are tiers of us
   int64_t tier_of;         ///< pool for which we are a tier
@@ -914,6 +914,11 @@ public:
   unsigned get_pg_num_mask() const { return pg_num_mask; }
   unsigned get_pgp_num_mask() const { return pgp_num_mask; }
 
+  // if pg_num is not a multiple of two, pgs are not equally sized.
+  // return, for a given pg, the fraction (denominator) of the total
+  // pool size that it represents.
+  unsigned get_pg_num_divisor(pg_t pgid) const;
+
   void set_pg_num(int p) {
     pg_num = p;
     calc_pg_masks();

diff --git a/src/test/test_osd_types.cc b/src/test/test_osd_types.cc
index bcc71c37bd136b24c683adddf939260dfbffb604..ed878695122f1e87abf6fb82871dee933ff175ed 100644 (file)
--- a/src/test/test_osd_types.cc
+++ b/src/test/test_osd_types.cc
@@ -1160,6 +1160,33 @@ TEST_F(ObjectContextTest, read_write_lock)
   
 }
 
+TEST(pg_pool_t_test, get_pg_num_divisor) {
+  pg_pool_t p;
+  p.set_pg_num(16);
+  p.set_pgp_num(16);
+
+  for (int i = 0; i < 16; ++i)
+    ASSERT_EQ(16u, p.get_pg_num_divisor(pg_t(i, 1)));
+
+  p.set_pg_num(12);
+  p.set_pgp_num(12);
+  //cout << "num " << p.get_pg_num()
+  //     << " mask " << p.get_pg_num_mask() << std::endl;
+  ASSERT_EQ(16u, p.get_pg_num_divisor(pg_t(0, 1)));
+  ASSERT_EQ(16u, p.get_pg_num_divisor(pg_t(1, 1)));
+  ASSERT_EQ(16u, p.get_pg_num_divisor(pg_t(2, 1)));
+  ASSERT_EQ(16u, p.get_pg_num_divisor(pg_t(3, 1)));
+  ASSERT_EQ(8u, p.get_pg_num_divisor(pg_t(4, 1)));
+  ASSERT_EQ(8u, p.get_pg_num_divisor(pg_t(5, 1)));
+  ASSERT_EQ(8u, p.get_pg_num_divisor(pg_t(6, 1)));
+  ASSERT_EQ(8u, p.get_pg_num_divisor(pg_t(7, 1)));
+  ASSERT_EQ(16u, p.get_pg_num_divisor(pg_t(8, 1)));
+  ASSERT_EQ(16u, p.get_pg_num_divisor(pg_t(9, 1)));
+  ASSERT_EQ(16u, p.get_pg_num_divisor(pg_t(10, 1)));
+  ASSERT_EQ(16u, p.get_pg_num_divisor(pg_t(11, 1)));
+}
+
+
 /*
  * Local Variables:
  * compile-command: "cd .. ;