PGPool::update: avoid expensive union_of

Achieve the same result using a swap (constant complexity),
and an assignment (linear complexity).

Signed-off-by: Zac Medico <zmedico@gmail.com>
(cherry picked from commit bf20b661cb6a6a33d9e93fb44ad1470f9f8245d2)

diff --git a/src/osd/PG.cc b/src/osd/PG.cc
index 04f2d92828d957a4fb1d931f5266ab7de9571926..1e32d202dae470701816e8ae016ce5cdeb47ba11 100644 (file)
--- a/src/osd/PG.cc
+++ b/src/osd/PG.cc
@@ -241,8 +241,9 @@ void PGPool::update(OSDMapRef map)
     interval_set<snapid_t> intersection;
     intersection.intersection_of(newly_removed_snaps, cached_removed_snaps);
     if (intersection == cached_removed_snaps) {
-        newly_removed_snaps.subtract(cached_removed_snaps);
-        cached_removed_snaps.union_of(newly_removed_snaps);
+        cached_removed_snaps.swap(newly_removed_snaps);
+        newly_removed_snaps = cached_removed_snaps;
+        newly_removed_snaps.subtract(intersection);
     } else {
         lgeneric_subdout(cct, osd, 0) << __func__
           << " cached_removed_snaps shrank from " << cached_removed_snaps