Changeset 75709 in webkit

Timestamp:

Jan 13, 2011 3:58:25 AM (13 years ago)

Author:

xan@webkit.org

Message:

2011-01-13 Xan Lopez <​xlopez@igalia.com>

Reviewed by Gavin Barraclough.

JIT requires VM overcommit (particularly on x86-64), Linux does not by default support this without swap?
​https://bugs.webkit.org/show_bug.cgi?id=42756

The FixedVMPool Allocator does not work well on systems where
allocating very large amounts of memory upfront is not reasonable,
like Linux without overcommit enabled. As a workaround, on Linux,
default to the values used in embedded environments (in the MB
range), and only jump to the GB range if we detect at runtime that
overcommit is enabled. Should fix crashes on Linux/x86_64 with
less than 3 or 4GB of RAM.

• jit/ExecutableAllocatorFixedVMPool.cpp: (JSC::FixedVMPoolAllocator::free): use new variables for VM pool size and coalesce limit. (JSC::ExecutableAllocator::isValid): swap the variables from embedded to generic values at runtime, on linux, if overcommit is enabled. (JSC::ExecutableAllocator::underMemoryPressure): use new variables for VM pool size and coalesce limit.

Location:

trunk/Source/JavaScriptCore

Files:

• ChangeLog (modified) (1 diff)
• jit/ExecutableAllocatorFixedVMPool.cpp (modified) (4 diffs)

trunk/Source/JavaScriptCore/ChangeLog

@@ +1 @@
+2011-01-13  Xan Lopez  <xlopez@igalia.com>
+
+        Reviewed by Gavin Barraclough.
+
+        JIT requires VM overcommit (particularly on x86-64), Linux does not by default support this without swap?
+        https://bugs.webkit.org/show_bug.cgi?id=42756
+
+        The FixedVMPool Allocator does not work well on systems where
+        allocating very large amounts of memory upfront is not reasonable,
+        like Linux without overcommit enabled. As a workaround, on Linux,
+        default to the values used in embedded environments (in the MB
+        range), and only jump to the GB range if we detect at runtime that
+        overcommit is enabled. Should fix crashes on Linux/x86_64 with
+        less than 3 or 4GB of RAM.
+
+        * jit/ExecutableAllocatorFixedVMPool.cpp:
+        (JSC::FixedVMPoolAllocator::free): use new variables for VM pool
+        size and coalesce limit.
+        (JSC::ExecutableAllocator::isValid): swap the variables from
+        embedded to generic values at runtime, on linux, if overcommit is
+        enabled.
+        (JSC::ExecutableAllocator::underMemoryPressure): use new variables
+        for VM pool size and coalesce limit.
+
 2011-01-12  Xan Lopez  <xlopez@igalia.com>
 

trunk/Source/JavaScriptCore/jit/ExecutableAllocatorFixedVMPool.cpp

@@ -39 +39 @@
 #include <wtf/VMTags.h>
 
-#if CPU(X86_64)
-    // These limits suitable on 64-bit platforms (particularly x86-64, where we require all jumps to have a 2Gb max range).
-    #define VM_POOL_SIZE (2u * 1024u * 1024u * 1024u) // 2Gb
-    #define COALESCE_LIMIT (16u * 1024u * 1024u) // 16Mb
+#if OS(LINUX)
+#include <stdio.h>
+#endif
+
+static const unsigned vmPoolSizeGeneric = 2u * 1024u * 1024u * 1024u; // 2Gb
+static const unsigned coalesceLimitGeneric = 16u * 1024u * 1024u; // 16Mb
+
+static const unsigned vmPoolSizeEmbedded = 32u * 1024u * 1024u; // 32Mb
+static const unsigned coalesceLimitEmbedded = 4u * 1024u * 1024u; // 4Mb
+
+#if CPU(X86_64) && !OS(LINUX)
+// These limits suitable on 64-bit platforms (particularly x86-64,
+// where we require all jumps to have a 2Gb max range). We don't
+// enable this by default on Linux, since it needs overcommit and
+// distros commonly disable that feature. We'll check the value
+// for the overcommit feature at runtime and re-assign the Generic
+// values if it's enabled.
+static unsigned vmPoolSize = vmPoolSizeGeneric; // 2Gb
+static unsigned coalesceLimit = coalesceLimitGeneric; // 16Mb
 #else
     // These limits are hopefully sensible on embedded platforms.
-    #define VM_POOL_SIZE (32u * 1024u * 1024u) // 32Mb
-    #define COALESCE_LIMIT (4u * 1024u * 1024u) // 4Mb
+static unsigned vmPoolSize = vmPoolSizeEmbedded; // 32Mb
+static unsigned coalesceLimit = coalesceLimitEmbedded; // 4Mb
 #endif
 
@@ -316 +331 @@
         // coalescing any neighboring fragments.
         m_countFreedSinceLastCoalesce += size;
-        if (m_countFreedSinceLastCoalesce >= COALESCE_LIMIT) {
+        if (m_countFreedSinceLastCoalesce >= coalesceLimit) {
             m_countFreedSinceLastCoalesce = 0;
             coalesceFreeSpace();
@@ -434 +449 @@
 static size_t allocatedCount = 0;
 
+#if OS(LINUX)
+static void maybeModifyVMPoolSize()
+{
+    FILE* fp = fopen("/proc/sys/vm/overcommit_memory", "r");
+    if (!fp)
+        return;
+
+    unsigned overcommit = 0;
+    fscanf(fp, "%u", &overcommit);
+    if (overcommit == 1) {
+        vmPoolSize = vmPoolSizeGeneric; // 2Gb
+        coalesceLimit = coalesceLimitGeneric; // 16Mb
+    }
+
+    fclose(fp);
+}
+#endif
+
 bool ExecutableAllocator::isValid() const
 {
     SpinLockHolder lock_holder(&spinlock);
-    if (!allocator)
-        allocator = new FixedVMPoolAllocator(JIT_ALLOCATOR_LARGE_ALLOC_SIZE, VM_POOL_SIZE);
+    if (!allocator) {
+#if OS(LINUX)
+        maybeModifyVMPoolSize();
+#endif
+        allocator = new FixedVMPoolAllocator(JIT_ALLOCATOR_LARGE_ALLOC_SIZE, vmPoolSize);
+    }
     return allocator->isValid();
 }
@@ -446 +483 @@
     // Technically we should take the spin lock here, but we don't care if we get stale data.
     // This is only really a heuristic anyway.
-    return allocatedCount > (VM_POOL_SIZE / 2);
+    return allocatedCount > (vmPoolSize / 2);
 }