From 8a0bf61c5a9d2c71399a6facb8d2da428abf2070 Mon Sep 17 00:00:00 2001
From: Kefu Chai <kchai@redhat.com>
Date: Tue, 27 Nov 2018 12:08:28 +0800
Subject: [PATCH] denc: only shallow_copy large-enough chunk for decoding

if the bl being decoded is not continous, shallow_copy() will do deep
copy under the hood. this introduces internal fragmentation when
decoding small objects in large non-contiguous bufferlist.

to alleviate this problem, we try to copy less if the object being
decoded is bounded.

Signed-off-by: Kefu Chai <kchai@redhat.com>
---
 src/include/denc.h         | 9 ++++++++-
 src/include/interval_set.h | 1 +
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/src/include/denc.h b/src/include/denc.h
index d4733f09c8499..081df4b665606 100644
--- a/src/include/denc.h
+++ b/src/include/denc.h
@@ -1592,7 +1592,14 @@ inline std::enable_if_t<traits::supported && !traits::featured> decode_nohead(
   if constexpr (traits::need_contiguous) {
     bufferptr tmp;
     auto t = p;
-    t.copy_shallow(p.get_bl().length() - p.get_off(), tmp);
+    if constexpr (denc_traits<typename T::value_type>::bounded) {
+      size_t element_size = 0;
+      typename T::value_type v;
+      denc_traits<typename T::value_type>::bound_encode(v, element_size);
+      t.copy_shallow(num * element_size, tmp);
+    } else {
+      t.copy_shallow(p.get_bl().length() - p.get_off(), tmp);
+    }
     auto cp = std::cbegin(tmp);
     traits::decode_nohead(num, o, cp);
     p.advance(cp.get_offset());
diff --git a/src/include/interval_set.h b/src/include/interval_set.h
index 825bcf2e4d787..4fb6be45a9e6b 100644
--- a/src/include/interval_set.h
+++ b/src/include/interval_set.h
@@ -33,6 +33,7 @@
 template<typename T, typename Map = std::map<T,T>>
 class interval_set {
  public:
+  using value_type = T;
 
   class const_iterator;
 
-- 
2.39.5