[Discardable Shared Memory] Adding Windows support.

base/memory/discardable_shared_memory.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/memory/discardable_shared_memory.h"
 
 #if defined(OS_POSIX) && !defined(OS_NACL)
 // For madvise() which is available on all POSIX compatible systems.
 #include <sys/mman.h>
 #endif
 
 #include <algorithm>
 
 #include "base/atomicops.h"
 #include "base/bits.h"
 #include "base/logging.h"
 #include "base/numerics/safe_math.h"
 #include "base/process/process_metrics.h"
 
 #if defined(OS_ANDROID)
 #include "third_party/ashmem/ashmem.h"
 #endif
 
+#if defined(OS_WIN)
+#include "base/win/windows_version.h"
+#endif
+
 namespace base {
 namespace {
 
 // Use a machine-sized pointer as atomic type. It will use the Atomic32 or
 // Atomic64 routines, depending on the architecture.
 typedef intptr_t AtomicType;
 typedef uintptr_t UAtomicType;
 
 // Template specialization for timestamp serialization/deserialization. This
 // is used to serialize timestamps using Unix time on systems where AtomicType
@@ skipping 173 matching lines @@
   locked_page_count_ += end - start;
 #if DCHECK_IS_ON()
   // Detect incorrect usage by keeping track of exactly what pages are locked.
   for (auto page = start; page < end; ++page) {
     auto result = locked_pages_.insert(page);
     DCHECK(result.second);
   }
   DCHECK_EQ(locked_pages_.size(), locked_page_count_);
 #endif
 
+// Pin pages if supported.
 #if defined(OS_ANDROID)
   SharedMemoryHandle handle = shared_memory_.handle();
   if (SharedMemory::IsHandleValid(handle)) {
     if (ashmem_pin_region(
             handle.fd, AlignToPageSize(sizeof(SharedState)) + offset, length)) {
       return PURGED;
     }
   }
+#elif defined(OS_WIN)
+  if (base::win::GetVersion() >= base::win::VERSION_WIN8) {
+    if (!VirtualAlloc(reinterpret_cast<char*>(shared_memory_.memory()) +
+                          AlignToPageSize(sizeof(SharedState)) + offset,
+                      length, MEM_RESET_UNDO, PAGE_READWRITE)) {
+      return PURGED;
+    }
+  }
 #endif
 
   return SUCCESS;
 }
 
 void DiscardableSharedMemory::Unlock(size_t offset, size_t length) {
   DCHECK_EQ(AlignToPageSize(offset), offset);
   DCHECK_EQ(AlignToPageSize(length), length);
 
   // Calls to this function must be synchronized properly.
   DFAKE_SCOPED_LOCK(thread_collision_warner_);
 
   // Zero for length means "everything onward".
   if (!length)
     length = AlignToPageSize(mapped_size_) - offset;
 
   DCHECK(shared_memory_.memory());
 
+// Unpin pages if supported.
 #if defined(OS_ANDROID)
   SharedMemoryHandle handle = shared_memory_.handle();
   if (SharedMemory::IsHandleValid(handle)) {
     if (ashmem_unpin_region(
             handle.fd, AlignToPageSize(sizeof(SharedState)) + offset, length)) {
       DPLOG(ERROR) << "ashmem_unpin_region() failed";
     }
   }
+#elif defined(OS_WIN)
+  if (base::win::GetVersion() >= base::win::VERSION_WIN8) {
+    if (!VirtualAlloc(reinterpret_cast<char*>(shared_memory_.memory()) +
+                          AlignToPageSize(sizeof(SharedState)) + offset,
+                      length, MEM_RESET, PAGE_READWRITE)) {
+      DPLOG(ERROR) << "VirtualAlloc() MEM_RESET failed in Unlock()";
+    }
 #endif
+}
 
   size_t start = offset / base::GetPageSize();
   size_t end = start + length / base::GetPageSize();
   DCHECK_LT(start, end);
   DCHECK_LE(end, AlignToPageSize(mapped_size_) / base::GetPageSize());
 
   // Remove pages from |locked_page_count_|.
   // Note: Unlocking a page that is not locked is an error.
   DCHECK_GE(locked_page_count_, end - start);
   locked_page_count_ -= end - start;
@@ skipping 71 matching lines @@
 #define MADV_PURGE_ARGUMENT MADV_FREE
 #endif
   // Advise the kernel to remove resources associated with purged pages.
   // Subsequent accesses of memory pages will succeed, but might result in
   // zero-fill-on-demand pages.
   if (madvise(reinterpret_cast<char*>(shared_memory_.memory()) +
                   AlignToPageSize(sizeof(SharedState)),
               AlignToPageSize(mapped_size_), MADV_PURGE_ARGUMENT)) {
     DPLOG(ERROR) << "madvise() failed";
   }
+#elif defined(OS_WIN)
+  // MEM_DECOMMIT the purged pages to release the physical storage,
+  // either in memory or in the paging file on disk.  Pages remain RESERVED.
+  // NOTE: this is the best that can be done from the browser, until the
+  // child/renderer notices the purge and releases its own handles.

[reveman, 2015/11/03 01:42:31]

nit: concepts such as browser and renderer process should not leak into base/.
if we need this comment here then maybe "purging process" instead of browser and
"client process" instead of child/renderer.

[penny, 2015/11/03 02:17:08]

Done.

+  if (!VirtualFree(reinterpret_cast<char*>(shared_memory_.memory()) +
+                       AlignToPageSize(sizeof(SharedState)),
+                   AlignToPageSize(mapped_size_), MEM_DECOMMIT)) {
+    DPLOG(ERROR) << "VirtualFree() MEM_DECOMMIT failed in Purge()";
+  }
 #endif
 
   last_known_usage_ = Time();
   return true;
 }
 
 bool DiscardableSharedMemory::IsMemoryResident() const {
   DCHECK(shared_memory_.memory());
 
   SharedState result(subtle::NoBarrier_Load(
@@ skipping 14 matching lines @@
 
 void DiscardableSharedMemory::Close() {
   shared_memory_.Close();
 }
 
 Time DiscardableSharedMemory::Now() const {
   return Time::Now();
 }
 
 }  // namespace base