diff --git a/src/include/interval_set.h b/src/include/interval_set.h
index a8446ad0808..67b7ac2e53e 100644
--- a/src/include/interval_set.h
+++ b/src/include/interval_set.h
@@ -286,6 +286,38 @@ class interval_set {
       }
     }
   }
+
+  bool subset_size_sym(const interval_set &b) const {
+    auto pa = m.cbegin(), pb = b.m.cbegin();
+    const auto a_end = m.cend(), b_end = b.m.cend();
+
+    while (pa != a_end && pb != b_end) {
+      while (pb->first + pb->second <= pa->first) {
+        ++pb;
+        if (pb == b_end)
+          return false;
+      }
+
+      if (*pa == *pb) {
+        do {
+          ++pa;
+          ++pb;
+        } while (pa != a_end && pb != b_end && *pa == *pb);
+        continue;
+      }
+
+      // interval begins before other
+      if (pa->first < pb->first)
+        return false;
+      // interval is longer than other
+      if (pa->first + pa->second > pb->first + pb->second)
+        return false;
+
+      ++pa;
+    }
+
+    return pa == a_end;
+  }
   
  public:
   bool operator==(const interval_set& other) const {
@@ -606,6 +638,21 @@ class interval_set {
   }
 
   bool subset_of(const interval_set &big) const {
+    if (!size())
+      return true;
+    if (size() > big.size())
+      return false;
+    if (range_end() > big.range_end())
+      return false;
+
+    /*
+     * Use the lower_bound algorithm for larger size ratios
+     * where it performs better, but not for smaller size
+     * ratios where sequential search performs better.
+     */
+    if (big.size() / size() < 10)
+      return subset_size_sym(big);
+
     for (typename std::map<T,T>::const_iterator i = m.begin();
          i != m.end();
          i++) 
diff --git a/src/osd/PG.cc b/src/osd/PG.cc
index f1c86047c92..432d536b621 100644
--- a/src/osd/PG.cc
+++ b/src/osd/PG.cc
@@ -237,12 +237,10 @@ void PGPool::update(OSDMapRef map)
     updated = true;
     if (pi->maybe_updated_removed_snaps(cached_removed_snaps)) {
       pi->build_removed_snaps(newly_removed_snaps);
-      interval_set<snapid_t> intersection;
-      intersection.intersection_of(newly_removed_snaps, cached_removed_snaps);
-      if (intersection == cached_removed_snaps) {
-          cached_removed_snaps.swap(newly_removed_snaps);
-          newly_removed_snaps = cached_removed_snaps;
-          newly_removed_snaps.subtract(intersection);
+      if (cached_removed_snaps.subset_of(newly_removed_snaps)) {
+          interval_set<snapid_t> removed_snaps = newly_removed_snaps;
+          newly_removed_snaps.subtract(cached_removed_snaps);
+          cached_removed_snaps.swap(removed_snaps);
       } else {
           lgeneric_subdout(cct, osd, 0) << __func__
             << " cached_removed_snaps shrank from " << cached_removed_snaps
diff --git a/src/test/common/test_interval_set.cc b/src/test/common/test_interval_set.cc
index 66a79a6e494..f44f35e316f 100644
--- a/src/test/common/test_interval_set.cc
+++ b/src/test/common/test_interval_set.cc
@@ -526,6 +526,37 @@ TYPED_TEST(IntervalSetTest, subset_of) {
 
   iset1.insert( 24, 1);
   ASSERT_FALSE(iset1.subset_of(iset2));
+
+  iset2.insert( 24, 1);
+  ASSERT_TRUE(iset1.subset_of(iset2));
+
+  iset1.insert( 30, 5);
+  ASSERT_FALSE(iset1.subset_of(iset2));
+
+  iset2.insert( 30, 5);
+  ASSERT_TRUE(iset1.subset_of(iset2));
+
+  iset2.erase( 30, 1);
+  ASSERT_FALSE(iset1.subset_of(iset2));
+
+  iset1.erase( 30, 1);
+  ASSERT_TRUE(iset1.subset_of(iset2));
+
+  iset2.erase( 34, 1);
+  ASSERT_FALSE(iset1.subset_of(iset2));
+
+  iset1.erase( 34, 1);
+  ASSERT_TRUE(iset1.subset_of(iset2));
+
+  iset1.insert( 40, 5);
+  ASSERT_FALSE(iset1.subset_of(iset2));
+
+  iset2.insert( 39, 7);
+  ASSERT_TRUE(iset1.subset_of(iset2));
+
+  iset1.insert( 50, 5);
+  iset2.insert( 55, 2);
+  ASSERT_FALSE(iset1.subset_of(iset2));
 }
 
 TYPED_TEST(IntervalSetTest, span_of) {