Add DiscardableMemoryAllocator to work around FD limit issue.

base/memory/discardable_memory_android.cc

 // Copyright (c) 2013 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_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"
 #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/posix/eintr_wrapper.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 char kAshmemAllocatorName[] = "DiscardableMemoryAllocator";
 
-// Total number of discardable memory in the process.
-int g_num_discardable_memory = 0;
+struct GlobalContext {
+  GlobalContext()
+      : ashmem_fd_limit(GetSoftFDLimit()),
+        allocator(kAshmemAllocatorName),
+        ashmem_fd_count_(0) {
+  }
 
-// Upper limit on the number of discardable memory to avoid hitting file
-// descriptor limit.
-const int kDiscardableMemoryNumLimit = 128;
+  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
+// DiscardableMemory::CreateLockedMemory() 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();
+}
+
+}  // namespace
+
+namespace internal {
+
+size_t AlignToNextPage(size_t size) {
+  const size_t kPageSize = 4096;

[willchan no longer on Chromium, 2013/11/28 06:16:37]

Is there any way to whitelist this for known architectures so if someone tries
to build this on an architecture that has a different page size, this will fail?
Also, what happens if/when Android starts using hugepages? I'm fine with not
solving these problems now, but I think it's be nice to make this code fail
loudly (compile failure?) when that happens in the future.

[Philippe, 2013/11/28 16:42:53]

Yeah good idea. I added a DCHECK. This is not ideal compared to a COMPILE_ASSERT
but it should fail early enough.

+  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) {
     DLOG(ERROR) << "ashmem_create_region() failed";
     return false;
   }
   file_util::ScopedFD fd_closer(&fd);
 
   const int err = ashmem_set_prot_region(fd, PROT_READ | PROT_WRITE);
   if (err < 0) {
     DLOG(ERROR) << "Error " << err << " when setting protection of ashmem";
     return false;
   }
 
   // There is a problem using MAP_PRIVATE here. As we are constantly calling
   // Lock() and Unlock(), data could get lost if they are not written to the
   // underlying file when Unlock() gets called.
   void* const address = mmap(
       NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
   if (address == MAP_FAILED) {
     DPLOG(ERROR) << "Failed to map memory.";
     return false;
   }
 
   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);
     return false;
   }
   return close(fd) == 0;
 }
 
 LockDiscardableMemoryStatus LockAshmemRegion(int fd,
                                              size_t off,
                                              size_t size,
                                              const void* address) {
   const int result = ashmem_pin_region(fd, off, size);
   DCHECK_EQ(0, mprotect(address, size, PROT_READ | PROT_WRITE));
   return result == ASHMEM_WAS_PURGED ?
       DISCARDABLE_MEMORY_PURGED : DISCARDABLE_MEMORY_SUCCESS;
 }
 
 bool UnlockAshmemRegion(int fd, size_t off, size_t size, const void* address) {
   const int failed = ashmem_unpin_region(fd, off, size);
   if (failed)
     DLOG(ERROR) << "Failed to unpin memory.";
   // This allows us to catch accesses to unlocked memory.
   DCHECK_EQ(0, mprotect(address, size, PROT_NONE));
   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;
 }
 
 // static
 scoped_ptr<DiscardableMemory> DiscardableMemory::CreateLockedMemory(
     size_t size) {
+  GlobalContext* const global_context = g_context.Pointer();
+  // Allocation can happen in two ways:
+  // - Each client-requested allocation is backed by an individual ashmem
+  // region. This allows to delete 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.
+  // - 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 physycal pages backing) individiual regions.
+  const bool use_allocator = GetCurrentNumberOfAshmemFDs() >
+      0.9 * global_context->ashmem_fd_limit;
+  if (use_allocator)
+    return global_context->allocator.Allocate(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::AlignToNextPage(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));
+      new DiscardableMemoryAndroidSimple(fd, address, size));
 }
 
 // static
 bool DiscardableMemory::PurgeForTestingSupported() {
   return false;
 }
 
 // static
 void DiscardableMemory::PurgeForTesting() {
   NOTIMPLEMENTED();
 }
 
 }  // namespace base