Changeset 286804 in webkit

Timestamp:

Dec 9, 2021, 2:56:06 PM (5 years ago)

Author:

keith_miller@apple.com

Message:

Reduce maximum mmap size for Structure regions to help placate ios
​https://bugs.webkit.org/show_bug.cgi?id=234091

Reviewed by Saam Barati.

Use mach_vm_map since that supports memory alignement so we don't have to map 2x desired address space then free then trim.

• wtf/PlatformHave.h:
• wtf/posix/OSAllocatorPOSIX.cpp:

(WTF::OSAllocator::reserveUncommittedAligned):

Location:

trunk/Source/WTF

Files:

• ChangeLog (modified) (1 diff)
• wtf/posix/OSAllocatorPOSIX.cpp (modified) (3 diffs)

trunk/Source/WTF/ChangeLog

@@ +1 @@
+2021-12-09  Keith Miller  <keith_miller@apple.com>
+
+        Reduce maximum mmap size for Structure regions to help placate ios
+        https://bugs.webkit.org/show_bug.cgi?id=234091
+
+        Reviewed by Saam Barati.
+
+        Use mach_vm_map since that supports memory alignement so we don't have to map 2x desired address space then free then trim.
+
+        * wtf/PlatformHave.h:
+        * wtf/posix/OSAllocatorPOSIX.cpp:
+        (WTF::OSAllocator::reserveUncommittedAligned):
+
 2021-12-09  Antti Koivisto  <antti@apple.com>
 

trunk/Source/WTF/wtf/posix/OSAllocatorPOSIX.cpp

@@ -39 +39 @@
 #define MAP_EXECUTABLE_FOR_JIT MAP_JIT
 #define MAP_EXECUTABLE_FOR_JIT_WITH_JIT_CAGE MAP_JIT
+#include <wtf/spi/cocoa/MachVMSPI.h>
 #else // OS(DARWIN)
 #define MAP_EXECUTABLE_FOR_JIT 0
@@ -74 +75 @@
 }
 
-
-// FIXME: Make a smarter version of this for Linux flavors that have aligned mmap.
 void* OSAllocator::reserveUncommittedAligned(size_t bytes, Usage usage, bool writable, bool executable, bool jitCageEnabled, bool includesGuardPages)
 {
     ASSERT(hasOneBitSet(bytes) && bytes >= pageSize());
+
+#if PLATFORM(MAC) || USE(APPLE_INTERNAL_SDK)
+    UNUSED_PARAM(usage); // Not supported for mach API.
+    ASSERT_UNUSED(includesGuardPages, !includesGuardPages);
+    ASSERT_UNUSED(jitCageEnabled, !jitCageEnabled); // Not supported for mach API.
+    vm_prot_t protections = VM_PROT_READ;
+    if (writable)
+        protections |= VM_PROT_WRITE;
+    if (executable)
+        protections |= VM_PROT_EXECUTE;
+
+    const vm_inherit_t childProcessInheritance = VM_INHERIT_DEFAULT;
+
+    void* aligned = nullptr;
+    const bool copy = false;
+    const int flags = VM_FLAGS_ANYWHERE;
+
+    kern_return_t result = mach_vm_map(mach_task_self(), reinterpret_cast<mach_vm_address_t*>(&aligned), bytes, bytes - 1, flags, MEMORY_OBJECT_NULL, 0, copy, protections, protections, childProcessInheritance);
+    RELEASE_ASSERT(result == KERN_SUCCESS, result, bytes);
+#if HAVE(MADV_FREE_REUSE)
+    if (aligned) {
+        // To support the "reserve then commit" model, we have to initially decommit.
+        while (madvise(aligned, bytes, MADV_FREE_REUSABLE) == -1 && errno == EAGAIN) { }
+    }
+#endif
+
+    return aligned;
+#else
     // Double the size so we can ensure enough mapped memory to get an aligned start.
     size_t mappedSize = bytes * 2;
@@ -96 +123 @@
 
     return aligned;
+#endif
 }