base: Improve DiscardableSharedMemory support for ashmem.

base: Improve DiscardableSharedMemory support for ashmem.

Locking can now succeed even when the range of pages has been
purged. This avoids unnecessary IPC as it reduces the need to
create new DiscardableSharedMemory instances when backed by ashmem.

BUG=429416
TEST=base_unittests --gtest_filter=DiscardableSharedMemoryTest*

Committed: https://crrev.com/876f863615f341236004e0c3cd47125311e4c2d4
Cr-Commit-Position: refs/heads/master@{#312992}

[reveman, 2015-01-23 21:21:29]

reveman@chromium.org changed reviewers:
+ avi@chromium.org

[Avi (use Gerrit), 2015-01-23 22:23:19]

lgtm

[reveman, 2015-01-23 23:25:41]

reveman@chromium.org changed reviewers:
+ danakj@chromium.org

[reveman, 2015-01-23 23:25:42]

+danakj for base/

[danakj, 2015-01-24 00:16:06]

https://codereview.chromium.org/871043003/diff/1/base/memory/discardable_shar...
File base/memory/discardable_shared_memory.h (right):

https://codereview.chromium.org/871043003/diff/1/base/memory/discardable_shar...
base/memory/discardable_shared_memory.h:60: // last known usage timestamp might
be out of date. Last know usage time
Last known

https://codereview.chromium.org/871043003/diff/1/base/memory/discardable_shar...
base/memory/discardable_shared_memory.h:61: // is updated to the actual last
usage timestamp if memory
wrapping

https://codereview.chromium.org/871043003/diff/1/content/child/child_discarda...
File content/child/child_discardable_shared_memory_manager.cc (right):

https://codereview.chromium.org/871043003/diff/1/content/child/child_discarda...
content/child/child_discardable_shared_memory_manager.cc:124: if (result ==
base::DiscardableSharedMemory::SUCCESS)
switch instead of series of ifs?

[reveman, 2015-01-24 00:27:48]

PTAL

https://codereview.chromium.org/871043003/diff/1/base/memory/discardable_shar...
File base/memory/discardable_shared_memory.h (right):

https://codereview.chromium.org/871043003/diff/1/base/memory/discardable_shar...
base/memory/discardable_shared_memory.h:60: // last known usage timestamp might
be out of date. Last know usage time
On 2015/01/24 00:16:06, danakj wrote:
> Last known

Done.

https://codereview.chromium.org/871043003/diff/1/base/memory/discardable_shar...
base/memory/discardable_shared_memory.h:61: // is updated to the actual last
usage timestamp if memory
On 2015/01/24 00:16:06, danakj wrote:
> wrapping

Done.

https://codereview.chromium.org/871043003/diff/1/content/child/child_discarda...
File content/child/child_discardable_shared_memory_manager.cc (right):

https://codereview.chromium.org/871043003/diff/1/content/child/child_discarda...
content/child/child_discardable_shared_memory_manager.cc:124: if (result ==
base::DiscardableSharedMemory::SUCCESS)
On 2015/01/24 00:16:06, danakj wrote:
> switch instead of series of ifs?

Good idea. Done.

[danakj, 2015-01-24 00:28:30]

LGTM

[reveman, 2015-01-24 01:45:59]

The CQ bit was checked by reveman@chromium.org

[commit-bot: I haz the power, 2015-01-24 01:47:03]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/871043003/40001

[commit-bot: I haz the power, 2015-01-24 02:04:04]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2015-01-24 02:05:41]

Patchset 3 (id:??) landed as
https://crrev.com/876f863615f341236004e0c3cd47125311e4c2d4
Cr-Commit-Position: refs/heads/master@{#312992}