commit 74e74f96a75209379facaf9d46f424c571b484a8
author Christopher Ferris <cferris@google.com> Wed Aug 02 17:54:27 2017 -0700
committer Christopher Ferris <cferris@google.com> Fri Aug 11 12:48:11 2017 -0700
tree 2099f2dc64374746e25f0d7df601b9257b172f43
parent af6a262020cc3f85e9c65e38b8dbd6959864cb79

Decrease size of LogBufferElements to 32 bytes.

- Remove virtual from the destructor.
- Remove mTag and derive it when calling getTag().
- Add a boolean mDropped to tell when a message is dropped.
- When dropping a message, and it contains valid tag data, reallocate
  the message to only contain the tag data.
- Add the packed tag to the class.

This saves about ~150K of PSS on a typical log stream since it moves the
size of the LogBufferElement from 48 bytes to 32 bytes which puts it in
a smaller bin.

Bug: 63792187

Test: Builds, unit tests pass.
Change-Id: Ia5afce343ea3d344fcecd78c648338e94f5c9312

logd/LogBufferElement.cpp

diff --git a/logd/LogBufferElement.cpp b/logd/LogBufferElement.cpp
index 381c974..f20ac45 100644
--- a/logd/LogBufferElement.cpp
+++ b/logd/LogBufferElement.cpp
@@ -41,22 +41,20 @@
       mTid(tid),
       mRealTime(realtime),
       mMsgLen(len),
-      mLogId(log_id) {
+      mLogId(log_id),
+      mDropped(false) {
     mMsg = new char[len];
     memcpy(mMsg, msg, len);
-    mTag = (isBinary() && (mMsgLen >= sizeof(uint32_t)))
-               ? le32toh(reinterpret_cast<android_event_header_t*>(mMsg)->tag)
-               : 0;
 }
 
 LogBufferElement::LogBufferElement(const LogBufferElement& elem)
-    : mTag(elem.mTag),
-      mUid(elem.mUid),
+    : mUid(elem.mUid),
       mPid(elem.mPid),
       mTid(elem.mTid),
       mRealTime(elem.mRealTime),
       mMsgLen(elem.mMsgLen),
-      mLogId(elem.mLogId) {
+      mLogId(elem.mLogId),
+      mDropped(elem.mDropped) {
     mMsg = new char[mMsgLen];
     memcpy(mMsg, elem.mMsg, mMsgLen);
 }
@@ -65,6 +63,32 @@
     delete[] mMsg;
 }
 
+uint32_t LogBufferElement::getTag() const {
+    return (isBinary() &&
+            ((mDropped && mMsg != nullptr) ||
+             (!mDropped && mMsgLen >= sizeof(android_event_header_t))))
+               ? reinterpret_cast<const android_event_header_t*>(mMsg)->tag
+               : 0;
+}
+
+unsigned short LogBufferElement::setDropped(unsigned short value) {
+    // The tag information is saved in mMsg data, if the tag is non-zero
+    // save only the information needed to get the tag.
+    if (getTag() != 0) {
+        if (mMsgLen > sizeof(android_event_header_t)) {
+            char* truncated_msg = new char[sizeof(android_event_header_t)];
+            memcpy(truncated_msg, mMsg, sizeof(android_event_header_t));
+            delete[] mMsg;
+            mMsg = truncated_msg;
+        }  // mMsgLen == sizeof(android_event_header_t), already at minimum.
+    } else {
+        delete[] mMsg;
+        mMsg = nullptr;
+    }
+    mDropped = true;
+    return mDroppedCount = value;
+}
+
 // caller must own and free character string
 char* android::tidToName(pid_t tid) {
     char* retval = NULL;
@@ -164,8 +188,8 @@
     // identical to below to calculate the buffer size required
     const char* type = lastSame ? "identical" : "expire";
     size_t len = snprintf(NULL, 0, format_uid, mUid, name ? name : "",
-                          commName ? commName : "", type, mDropped,
-                          (mDropped > 1) ? "s" : "");
+                          commName ? commName : "", type, getDropped(),
+                          (getDropped() > 1) ? "s" : "");
 
     size_t hdrLen;
     if (isBinary()) {
@@ -196,8 +220,8 @@
     }
 
     snprintf(buffer + hdrLen, len + 1, format_uid, mUid, name ? name : "",
-             commName ? commName : "", type, mDropped,
-             (mDropped > 1) ? "s" : "");
+             commName ? commName : "", type, getDropped(),
+             (getDropped() > 1) ? "s" : "");
     free(const_cast<char*>(name));
     free(const_cast<char*>(commName));
 
@@ -225,7 +249,7 @@
 
     char* buffer = NULL;
 
-    if (!mMsg) {
+    if (mDropped) {
         entry.len = populateDroppedMessage(buffer, parent, lastSame);
         if (!entry.len) return mRealTime;
         iovec[1].iov_base = buffer;