Changeset 244506 in webkit

Timestamp:

Apr 22, 2019 11:35:04 AM (5 years ago)

Author:

ysuzuki@apple.com

Message:

[JSC] Use volatile load to populate backing page in MarkedBlock::Footer instead of using holdLock
​https://bugs.webkit.org/show_bug.cgi?id=197152

Reviewed by Saam Barati.

Emit volatile load instead of using holdLock to populate backing page in MarkedBlock::Footer.

• heap/BlockDirectory.cpp:

(JSC::BlockDirectory::isPagedOut):

• heap/MarkedBlock.h:

(JSC::MarkedBlock::populatePage const):

Location:

trunk/Source/JavaScriptCore

Files:

• ChangeLog (modified) (1 diff)
• heap/BlockDirectory.cpp (modified) (1 diff)
• heap/MarkedBlock.h (modified) (1 diff)

trunk/Source/JavaScriptCore/ChangeLog

@@ +1 @@
+2019-04-22  Yusuke Suzuki  <ysuzuki@apple.com>
+
+        [JSC] Use volatile load to populate backing page in MarkedBlock::Footer instead of using holdLock
+        https://bugs.webkit.org/show_bug.cgi?id=197152
+
+        Reviewed by Saam Barati.
+
+        Emit volatile load instead of using holdLock to populate backing page in MarkedBlock::Footer.
+
+        * heap/BlockDirectory.cpp:
+        (JSC::BlockDirectory::isPagedOut):
+        * heap/MarkedBlock.h:
+        (JSC::MarkedBlock::populatePage const):
+
 2019-04-22  Yusuke Suzuki  <ysuzuki@apple.com>
 

trunk/Source/JavaScriptCore/heap/BlockDirectory.cpp

@@ -62 +62 @@
     unsigned itersSinceLastTimeCheck = 0;
     for (auto* block : m_blocks) {
-        if (block) {
-            // We take and drop the lock as a way of touching that page of memory.
-            // FIXME: should we instead do a cheaper thing like a volatile load in the page?
-            (void) holdLock(block->block().lock());
-        }
+        if (block)
+            block->block().populatePage();
         ++itersSinceLastTimeCheck;
         if (itersSinceLastTimeCheck >= Heap::s_timeCheckResolution) {

trunk/Source/JavaScriptCore/heap/MarkedBlock.h

@@ -375 +375 @@
     
     Subspace* subspace() const { return footer().m_subspace; }
+
+    void populatePage() const
+    {
+        *bitwise_cast<volatile uint8_t*>(&footer());
+    }
     
     static constexpr size_t offsetOfFooter = endAtom * atomSize;