[trafficserver] branch 8.1.x updated: Coalesce empty objects in HdrHeap

[zwoop]

This is an automated email from the ASF dual-hosted git repository.

zwoop pushed a commit to branch 8.1.x
in repository https://gitbox.apache.org/repos/asf/trafficserver.git


The following commit(s) were added to refs/heads/8.1.x by this push:
     new ec0f5f9  Coalesce empty objects in HdrHeap
ec0f5f9 is described below

commit ec0f5f93947eb8d515a42f74b143b027868def4a
Author: Masaori Koshiba <masa...@apache.org>
AuthorDate: Tue Jun 25 09:25:15 2019 +0900

    Coalesce empty objects in HdrHeap
    
    HdrHeap could be filled by `HDR_HEAP_OBJ_EMPTY` type objects in some cases 
especially HPACK.
    In this situation, `HdrHeap::required_space_for_evacuation()` & 
`HdrHeap::evacuate_from_str_heaps()`
    could be slow because these functions always walk through `HdrHeapObjImpl` 
one by one.
    Coalescing empty objects next to each other can reduce number of objects 
and mitigate this issue.
    
    (cherry picked from commit 8461afa927471988753f10a286cfac4cef3dbd88)
    
    Conflicts:
        proxy/hdrs/HdrHeap.cc
---
 proxy/hdrs/HdrHeap.cc | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/proxy/hdrs/HdrHeap.cc b/proxy/hdrs/HdrHeap.cc
index 0a8831f..9268104 100644
--- a/proxy/hdrs/HdrHeap.cc
+++ b/proxy/hdrs/HdrHeap.cc
@@ -37,7 +37,8 @@
 #include "HTTP.h"
 #include "I_EventSystem.h"
 
-#define MAX_LOST_STR_SPACE 1024
+static constexpr size_t MAX_LOST_STR_SPACE        = 1024;
+static constexpr uint32_t MAX_HDR_HEAP_OBJ_LENGTH = (1 << 20) - 1; ///< 
m_length is 20 bit
 
 Allocator hdrHeapAllocator("hdrHeap", HDR_HEAP_DEFAULT_SIZE);
 static HdrHeap proto_heap;
@@ -440,7 +441,8 @@ HdrHeap::required_space_for_evacuation()
   size_t ret = 0;
   HdrHeap *h = this;
   while (h) {
-    char *data = h->m_data_start;
+    char *data               = h->m_data_start;
+    HdrHeapObjImpl *prev_obj = nullptr;
 
     while (data < h->m_free_start) {
       HdrHeapObjImpl *obj = (HdrHeapObjImpl *)data;
@@ -465,6 +467,19 @@ HdrHeap::required_space_for_evacuation()
       default:
         ink_release_assert(0);
       }
+
+      // coalesce empty objects next to each other
+      if (obj->m_type == HDR_HEAP_OBJ_EMPTY) {
+        if (prev_obj != nullptr && prev_obj->m_length < 
(MAX_HDR_HEAP_OBJ_LENGTH - obj->m_length)) {
+          prev_obj->m_length += obj->m_length;
+          ink_release_assert(prev_obj->m_length > 0);
+        } else {
+          prev_obj = obj;
+        }
+      } else {
+        prev_obj = nullptr;
+      }
+
       data = data + obj->m_length;
     }
     h = h->m_next;