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 8fee53e1d6cd388426a7e2542c839b5e46cc458d..7e84967055f1ba9d35f8c6efaeb84b12833586ad 100644
--- a/base/memory/discardable_memory_android.cc
+++ b/base/memory/discardable_memory_android.cc
@@ -2,39 +2,139 @@
 // 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 <limits>
+
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/file_util.h"
 #include "base/lazy_instance.h"
 #include "base/logging.h"
+#include "base/memory/discardable_memory.h"
+#include "base/memory/discardable_memory_allocator_android.h"
 #include "base/synchronization/lock.h"
 #include "third_party/ashmem/ashmem.h"
 
 namespace base {
 namespace {
 
-// Protects |g_num_discardable_memory| below.
-base::LazyInstance<base::Lock>::Leaky g_discardable_memory_lock =
-    LAZY_INSTANCE_INITIALIZER;
+const size_t kPageSize = 4096;
+
+const char kAshmemAllocatorName[] = "DiscardableMemoryAllocator";
+
+struct GlobalContext {
+  GlobalContext()
+      : ashmem_fd_limit(GetSoftFDLimit()),
+        allocator(kAshmemAllocatorName),
+        ashmem_fd_count_(0) {
+  }
+
+  const int ashmem_fd_limit;
+  internal::DiscardableMemoryAllocator allocator;
+  Lock lock;
+
+  int ashmem_fd_count() const {
+    lock.AssertAcquired();
+    return ashmem_fd_count_;
+  }
+
+  void decrement_ashmem_fd_count() {
+    lock.AssertAcquired();
+    --ashmem_fd_count_;
+  }
+
+  void increment_ashmem_fd_count() {
+    lock.AssertAcquired();
+    ++ashmem_fd_count_;
+  }
+
+ 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;
+  }
+
+  int ashmem_fd_count_;
+};
+
+LazyInstance<GlobalContext>::Leaky g_context = LAZY_INSTANCE_INITIALIZER;
+
+// This is the default implementation of DiscardableMemory on Android which is
+// used when file descriptor usage is under the soft limit. When file descriptor
+// usage gets too high the discardable memory allocator is used instead. See
+// ShouldUseAllocator() below for more details.
+class DiscardableMemoryAndroidSimple : public DiscardableMemory {
+ public:
+  DiscardableMemoryAndroidSimple(int fd, void* address, size_t size)
+      : fd_(fd),
+        memory_(address),
+        size_(size) {
+    DCHECK_GE(fd_, 0);
+    DCHECK(memory_);
+  }
+
+  virtual ~DiscardableMemoryAndroidSimple() {
+    internal::CloseAshmemRegion(fd_, size_, memory_);
+  }
+
+  // DiscardableMemory:
+  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(DiscardableMemoryAndroidSimple);
+};
+
+int GetCurrentNumberOfAshmemFDs() {
+  AutoLock lock(g_context.Get().lock);
+  return g_context.Get().ashmem_fd_count();
+}
 
-// Total number of discardable memory in the process.
-int g_num_discardable_memory = 0;
+// Returns whether the provided size can be safely page-aligned (without causing
+// an overflow).
+bool CheckSizeCanBeAlignedToNextPage(size_t size) {
+  return size <= std::numeric_limits<size_t>::max() - kPageSize + 1;
+}
 
-// Upper limit on the number of discardable memory to avoid hitting file
-// descriptor limit.
-const int kDiscardableMemoryNumLimit = 128;
+}  // namespace
+
+namespace internal {
+
+size_t AlignToNextPage(size_t size) {
+  DCHECK_EQ(static_cast<int>(kPageSize), getpagesize());
+  DCHECK(CheckSizeCanBeAlignedToNextPage(size));
+  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)
+  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) {
@@ -60,15 +160,15 @@ bool CreateAshmemRegion(const char* name,
   }
 
   ignore_result(fd_closer.release());
-  ++g_num_discardable_memory;
+  g_context.Get().increment_ashmem_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;
+bool CloseAshmemRegion(int fd, size_t size, void* address) {
+  AutoLock lock(g_context.Get().lock);
+  g_context.Get().decrement_ashmem_fd_count();
   if (munmap(address, size) == -1) {
     DPLOG(ERROR) << "Failed to unmap memory.";
     close(fd);
@@ -96,62 +196,54 @@ 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_;
-
-  DISALLOW_COPY_AND_ASSIGN(DiscardableMemoryAndroid);
-};
-
-}  // namespace
+}  // namespace internal
 
 // static
 bool DiscardableMemory::SupportedNatively() {
   return true;
 }
 
+// Allocation can happen in two ways:
+// - Each client-requested allocation is backed by an individual ashmem region.
+// This allows deleting ashmem regions individually by closing the ashmem file
+// descriptor. This is the default path that is taken when file descriptor usage
+// allows us to do so or when the allocation size would require and entire
+// ashmem region.
+// - Allocations are performed by the global allocator when file descriptor
+// usage gets too high. This still allows unpinning but does not allow deleting
+// (i.e. releasing the physical pages backing) individual regions.
+//
+// TODO(pliard): consider tuning the size threshold used below. For instance we
+// might want to make it a fraction of kMinAshmemRegionSize and also
+// systematically have small allocations go through the allocator to let big
+// allocations systematically go through individual ashmem regions.
+//
 // static
 scoped_ptr<DiscardableMemory> DiscardableMemory::CreateLockedMemory(
     size_t size) {
+  if (!CheckSizeCanBeAlignedToNextPage(size))
+    return scoped_ptr<DiscardableMemory>();
   // 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;
-  int fd;
-  void* address;
-  if (!CreateAshmemRegion("", size, &fd, &address))
-    return scoped_ptr<DiscardableMemory>();
-  return scoped_ptr<DiscardableMemory>(
-      new DiscardableMemoryAndroid(fd, address, size));
+  const size_t aligned_size = internal::AlignToNextPage(size);
+  // Note that the following code is slightly racy. The worst that can happen in
+  // practice though is taking the wrong decision (e.g. using the allocator
+  // rather than DiscardableMemoryAndroidSimple). Moreover keeping the lock
+  // acquired for the whole allocation would cause a deadlock when the allocator
+  // tries to create an ashmem region.
+  const size_t kAllocatorRegionSize =
+      internal::DiscardableMemoryAllocator::kMinAshmemRegionSize;
+  GlobalContext* const global_context = g_context.Pointer();
+  if (aligned_size >= kAllocatorRegionSize ||
+      GetCurrentNumberOfAshmemFDs() < 0.9 * global_context->ashmem_fd_limit) {
+    int fd;
+    void* address;
+    if (internal::CreateAshmemRegion("", aligned_size, &fd, &address)) {
+      return scoped_ptr<DiscardableMemory>(
+          new DiscardableMemoryAndroidSimple(fd, address, aligned_size));
+    }
+  }
+  return global_context->allocator.Allocate(size);
 }
 
 // static