Add DiscardableMemoryAllocator to work around FD limit issue.

base/memory/discardable_memory_android.cc

Index: base/memory/discardable_memory_android.cc
diff --git a/base/memory/discardable_memory_android.cc b/base/memory/discardable_memory_android.cc
index b88a13611b9c7a0488a4fd6a76751201e4b1bdf5..b2ec9bf69855f7522682cc3d8b76c887650348d1 100644
--- a/base/memory/discardable_memory_android.cc
+++ b/base/memory/discardable_memory_android.cc
@@ -2,9 +2,11 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "base/memory/discardable_memory.h"
+#include "base/memory/discardable_memory_android.h"
 
 #include <sys/mman.h>
+#include <sys/resource.h>
+#include <sys/time.h>
 #include <unistd.h>
 
 #include "base/basictypes.h"
@@ -12,6 +14,7 @@
 #include "base/file_util.h"
 #include "base/lazy_instance.h"
 #include "base/logging.h"
+#include "base/memory/discardable_memory.h"
 #include "base/posix/eintr_wrapper.h"
 #include "base/synchronization/lock.h"
 #include "third_party/ashmem/ashmem.h"
@@ -19,23 +22,96 @@
 namespace base {
 namespace {
 
-// Protects |g_num_discardable_memory| below.
-base::LazyInstance<base::Lock>::Leaky g_discardable_memory_lock =
-    LAZY_INSTANCE_INITIALIZER;
+struct GlobalContext {
+  GlobalContext() : ashmem_fd_limit(GetSoftFDLimit()), ashmem_fd_count_(0) {}
+
+  const int ashmem_fd_limit;
+  base::Lock lock;
+
+  int ashmem_fd_count() const {
+    lock.AssertAcquired();
+    return ashmem_fd_count_;
+  }
+
+  void decrement_ahmem_fd_count() {
+    lock.AssertAcquired();
+    --ashmem_fd_count_;
+  }
+
+  void increment_ahmem_fd_count() {
+    lock.AssertAcquired();
+    ++ashmem_fd_count_;
+  }
 
-// Total number of discardable memory in the process.
-int g_num_discardable_memory = 0;
+ private:
+  static int GetSoftFDLimit() {
+    struct rlimit limit_info;
+    if (getrlimit(RLIMIT_NOFILE, &limit_info) != 0)
+      return 128;
+    // Allow 25% of file descriptor capacity for ashmem.
+    return limit_info.rlim_cur / 4;
+  }
 
-// Upper limit on the number of discardable memory to avoid hitting file
-// descriptor limit.
-const int kDiscardableMemoryNumLimit = 128;
+  int ashmem_fd_count_;
+};
+
+base::LazyInstance<GlobalContext>::Leaky g_context = LAZY_INSTANCE_INITIALIZER;
+
+class DiscardableMemoryAndroid : public DiscardableMemory {
+ public:
+  DiscardableMemoryAndroid(int fd, void* address, size_t size)
+      : fd_(fd),
+        memory_(address),
+        size_(size) {
+    DCHECK_GE(fd_, 0);
+    DCHECK(memory_);
+  }
+
+  virtual ~DiscardableMemoryAndroid() {
+    internal::DeleteAshmemRegion(fd_, size_, memory_);
+  }
+
+  // DiscardableMemory:
+  virtual size_t Size() const OVERRIDE {
+    return size_;
+  }
+
+  virtual LockDiscardableMemoryStatus Lock() OVERRIDE {
+    return internal::LockAshmemRegion(fd_, 0, size_, memory_);
+  }
+
+  virtual void Unlock() OVERRIDE {
+    internal::UnlockAshmemRegion(fd_, 0, size_, memory_);
+  }
+
+  virtual void* Memory() const OVERRIDE {
+    return memory_;
+  }
+
+ private:
+  const int fd_;
+  void* const memory_;
+  const size_t size_;
+
+  DISALLOW_COPY_AND_ASSIGN(DiscardableMemoryAndroid);
+};
+
+}  // namespace
+
+namespace internal {
+
+size_t PageAlign(size_t size) {

[pasko, 2013/10/22 20:14:29]

nit: naming: this is not just aligning to page boundary, but rather
AlignToNextPage

+  const size_t kPageSize = 4096;
+  const size_t mask = ~(kPageSize - 1);
+  return (size + kPageSize - 1) & mask;
+}
 
 bool CreateAshmemRegion(const char* name,
                         size_t size,
                         int* out_fd,
                         void** out_address) {
-  base::AutoLock lock(g_discardable_memory_lock.Get());
-  if (g_num_discardable_memory + 1 > kDiscardableMemoryNumLimit)
+  base::AutoLock lock(g_context.Get().lock);
+  if (g_context.Get().ashmem_fd_count() + 1 > g_context.Get().ashmem_fd_limit)
     return false;
   int fd = ashmem_create_region(name, size);
   if (fd < 0) {
@@ -61,15 +137,15 @@ bool CreateAshmemRegion(const char* name,
   }
 
   ignore_result(fd_closer.release());
-  ++g_num_discardable_memory;
+  g_context.Get().increment_ahmem_fd_count();
   *out_fd = fd;
   *out_address = address;
   return true;
 }
 
 bool DeleteAshmemRegion(int fd, size_t size, void* address) {
-  base::AutoLock lock(g_discardable_memory_lock.Get());
-  --g_num_discardable_memory;
+  base::AutoLock lock(g_context.Get().lock);
+  g_context.Get().decrement_ahmem_fd_count();
   if (munmap(address, size) == -1) {
     DPLOG(ERROR) << "Failed to unmap memory.";
     close(fd);
@@ -97,42 +173,16 @@ bool UnlockAshmemRegion(int fd, size_t off, size_t size, const void* address) {
   return !failed;
 }
 
-class DiscardableMemoryAndroid : public DiscardableMemory {
- public:
-  DiscardableMemoryAndroid(int fd, void* address, size_t size)
-      : fd_(fd),
-        memory_(address),
-        size_(size) {
-    DCHECK_GE(fd_, 0);
-    DCHECK(memory_);
-  }
-
-  virtual ~DiscardableMemoryAndroid() {
-    DeleteAshmemRegion(fd_, size_, memory_);
-  }
-
-  // DiscardableMemory:
-  virtual LockDiscardableMemoryStatus Lock() OVERRIDE {
-    return LockAshmemRegion(fd_, 0, size_, memory_);
-  }
-
-  virtual void Unlock() OVERRIDE {
-    UnlockAshmemRegion(fd_, 0, size_, memory_);
-  }
-
-  virtual void* Memory() const OVERRIDE {
-    return memory_;
-  }
-
- private:
-  const int fd_;
-  void* const memory_;
-  const size_t size_;
+int GetAshmemFDLimit() {
+  return g_context.Get().ashmem_fd_limit;
+}
 
-  DISALLOW_COPY_AND_ASSIGN(DiscardableMemoryAndroid);
-};
+int GetCurrentNumberOfAshmemFDs() {
+  base::AutoLock lock(g_context.Get().lock);
+  return g_context.Get().ashmem_fd_count();
+}
 
-}  // namespace
+}  // namespace internal
 
 // static
 bool DiscardableMemory::Supported() {
@@ -144,12 +194,10 @@ scoped_ptr<DiscardableMemory> DiscardableMemory::CreateLockedMemory(
     size_t size) {
   // Pinning & unpinning works with page granularity therefore align the size
   // upfront.
-  const size_t kPageSize = 4096;
-  const size_t mask = ~(kPageSize - 1);
-  size = (size + kPageSize - 1) & mask;
+  size = internal::PageAlign(size);
   int fd;
   void* address;
-  if (!CreateAshmemRegion("", size, &fd, &address))
+  if (!internal::CreateAshmemRegion("", size, &fd, &address))
     return scoped_ptr<DiscardableMemory>();
   return scoped_ptr<DiscardableMemory>(
       new DiscardableMemoryAndroid(fd, address, size));