Zero-initialize persistent heap vector inline backing buffers.

Zero-initialize persistent heap vector inline backing buffers.

A persistent heap collection object is allocated off-heap,
along with its inlined buffer (if any.)

For heap-allocated backing buffers (inlined in a heap vector or
separate), the Oilpan allocator will provide a zero-initialized
chunk of memory to use. Consequently the invariant initially
holds that unused slots of the backing buffer are all zero initialized
-- something needed for precise tracing during GC marking

To have that invariant hold for the persistent heap vectors also,
we have to explicitly clear out the inline backing buffers on
(off-heap) allocation.

R=haraken
BUG=420515
Committed: https://crrev.com/641847a603e69022bb65d5a466c0836269c63e9b
Cr-Commit-Position: refs/heads/master@{#356014}

[sof, 2015-10-25 15:12:01]

please take a look.

Takes care of the cause of this crasher,


https://storage.googleapis.com/chromium-layout-test-archives/WebKit_Linux_Oil...

i.e., (off)heap allocated objects having PersistentHeapVector<> part objects.

[sof, 2015-10-25 18:18:19]

The CQ bit was checked by sigbjornf@opera.com to run a CQ dry run

[commit-bot: I haz the power, 2015-10-25 18:18:27]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1410223006/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1410223006/20001

[commit-bot: I haz the power, 2015-10-25 19:13:30]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-10-25 19:13:31]

Dry run: This issue passed the CQ dry run.

[haraken, 2015-10-26 06:47:07]

haraken@chromium.org changed reviewers:
+ haraken@chromium.org

[haraken, 2015-10-26 06:47:07]

LGTM

[sof, 2015-10-26 07:03:18]

Description was changed from

==========
Zero-initialize persistent heap vector inline backing buffers.

A persistent heap collection object is allocated off-heap,
along with its inlined buffer (if any.)

For heap-allocated backing buffers (inlined in a heap vector or
separate), the Oilpan allocator will provide a zero-initialized
chunk of memory to use. Consequently the invariant initially
holds that unused slots of the backing buffer are all zero initialized
-- something needed for precise tracing during GC marking

To have that invariant hold for the persistent heap vectors also,
we have to explicitly clear out the inline backing buffers on
(off-heap) allocation.

R=oilpan-reviews
BUG=420515
==========

to

==========
Zero-initialize persistent heap vector inline backing buffers.

A persistent heap collection object is allocated off-heap,
along with its inlined buffer (if any.)

For heap-allocated backing buffers (inlined in a heap vector or
separate), the Oilpan allocator will provide a zero-initialized
chunk of memory to use. Consequently the invariant initially
holds that unused slots of the backing buffer are all zero initialized
-- something needed for precise tracing during GC marking

To have that invariant hold for the persistent heap vectors also,
we have to explicitly clear out the inline backing buffers on
(off-heap) allocation.

R=haraken
BUG=420515
==========

[sof, 2015-10-26 07:03:26]

The CQ bit was checked by sigbjornf@opera.com

[commit-bot: I haz the power, 2015-10-26 07:03:37]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1410223006/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1410223006/20001

[commit-bot: I haz the power, 2015-10-26 07:08:32]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-10-26 07:09:37]

Patchset 2 (id:??) landed as
https://crrev.com/641847a603e69022bb65d5a466c0836269c63e9b
Cr-Commit-Position: refs/heads/master@{#356014}