If sweeping is in progress then we need to filter out slots in free space after
array trimming, because the sweeper will add the free space into free list.
This CL also fixes a bug in SlotSet::RemoveRange.
BUG=chromium:587004
LOG=NO
TBR=hpayer@chromium.org
Review URL: https://codereview.chromium.org/1701963003
Cr-Commit-Position: refs/heads/master@{#34071}
This change expands allocation sampling to include old, map, code, and large object spaces. This involved refactoring much of the observation logic out of NewSpace into Space and overriding as needed in sub-classes.
Additionally, the sampling heap profiler now maintains a pair of heap observers. One observer is used for observing new space and resetting the inline allocation limit to be periodically notified of allocations. The other observes allocation across the other spaces where there is no additional work required to observe allocations.
Tests have been updated to ensure that allocations are observed correctly for Paged and LargeObject spaces.
R=ofrobots@google.com, hpayer@chromium.org, ulan@chromium.org
BUG=
Review URL: https://codereview.chromium.org/1625753002
Cr-Commit-Position: refs/heads/master@{#33959}
Preparing the young generation for (real) non-contiguous backing memory, this
change removes object masks that are used to compute containment in semi and new
space. The masks are replaced by lookups for object tags and page headers, where
possible.
Details:
- Use the fast checks (page header lookups) for containment in regular code.
- Use the slow version that masks out the page start adress and iterates all
pages of a space for debugging/verification.
- The slow version works for off-heap/unmapped memory.
- Encapsulate all checks for the old->new barrier in Heap::RecordWrite().
BUG=chromium:581412
LOG=N
Review URL: https://codereview.chromium.org/1632913003
Cr-Commit-Position: refs/heads/master@{#33857}
The flag in question is a debug-only flag supported by full-codegen and
Crankshaft only. In it's current form there are some unresolved issues:
- The flag is defeated by inlining in Crankshaft.
- The flag is not supported by TurboFan.
- The flag is not supported by Ignition.
Instead of addressing the above issues and increasing maintenance cost
for all backends and also given the "slim" test coverage, this CL fully
removes the support from all backends.
R=bmeurer@chromium.org,jkummerow@chromium.org
Review URL: https://codereview.chromium.org/1676263002
Cr-Commit-Position: refs/heads/master@{#33817}
Reason for revert:
Must revert for now due to chromium api natives issues.
Original issue's description:
> Type Feedback Vector lives in the closure
>
> (RELAND: the problem before was a missing write barrier for adding the code
> entry to the new closure. It's been addressed with a new macro instruction
> and test. The only change to this CL is the addition of two calls to
> __ RecordWriteCodeEntryField() in the platform CompileLazy builtin.)
>
> We get less "pollution" of type feedback if we have one vector per native
> context, rather than one for the whole system. This CL moves the vector
> appropriately.
>
> We rely more heavily on the Optimized Code Map in the SharedFunctionInfo. The
> vector actually lives in the first slot of the literals array (indeed there is
> great commonality between those arrays, they can be thought of as the same
> thing). So we make greater effort to ensure there is a valid literals array
> after compilation.
>
> This meant, for performance reasons, that we needed to extend
> FastNewClosureStub to support creating closures with literals. And ultimately,
> it drove us to move the optimized code map lookup out of FastNewClosureStub
> and into the compile lazy builtin.
>
> The heap change is trivial so I TBR Hannes for it...
> Also, Yang has had a look at the debugger changes already and approved 'em. So he is TBR style too.
> And Benedikt reviewed it as well.
>
> TBR=hpayer@chromium.org, yangguo@chromium.org, bmeurer@chromium.org
>
> BUG=
>
> Committed: https://crrev.com/bb31db3ad6de16f86a61f6c7bbfd3274e3d957b5
> Cr-Commit-Position: refs/heads/master@{#33741}
TBR=bmeurer@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=
Review URL: https://codereview.chromium.org/1670813005
Cr-Commit-Position: refs/heads/master@{#33766}
(RELAND: the problem before was a missing write barrier for adding the code
entry to the new closure. It's been addressed with a new macro instruction
and test. The only change to this CL is the addition of two calls to
__ RecordWriteCodeEntryField() in the platform CompileLazy builtin.)
We get less "pollution" of type feedback if we have one vector per native
context, rather than one for the whole system. This CL moves the vector
appropriately.
We rely more heavily on the Optimized Code Map in the SharedFunctionInfo. The
vector actually lives in the first slot of the literals array (indeed there is
great commonality between those arrays, they can be thought of as the same
thing). So we make greater effort to ensure there is a valid literals array
after compilation.
This meant, for performance reasons, that we needed to extend
FastNewClosureStub to support creating closures with literals. And ultimately,
it drove us to move the optimized code map lookup out of FastNewClosureStub
and into the compile lazy builtin.
The heap change is trivial so I TBR Hannes for it...
Also, Yang has had a look at the debugger changes already and approved 'em. So he is TBR style too.
And Benedikt reviewed it as well.
TBR=hpayer@chromium.org, yangguo@chromium.org, bmeurer@chromium.org
BUG=
Review URL: https://codereview.chromium.org/1668103002
Cr-Commit-Position: refs/heads/master@{#33741}
Reason for revert:
Bisection results show that this was not the culprit.
Original issue's description:
> Revert of [heap] Simplify distribution of remaining memory during sweeping & compaction (patchset #2 id:80001 of https://codereview.chromium.org/1653973003/ )
>
> Reason for revert:
> Very likely blocking roll: https://codereview.chromium.org/1652413003/
>
> Original issue's description:
> > [heap] Simplify distribution of remaining memory during sweeping & compaction
> >
> > BUG=chromium:524425
> > LOG=N
> >
> > Committed: https://crrev.com/f72923526ccaa8faef5c977267b0c074c4a44dfa
> > Cr-Commit-Position: refs/heads/master@{#33668}
>
> TBR=hpayer@chromium.org,mlippautz@chromium.org
> # Skipping CQ checks because original CL landed less than 1 days ago.
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=chromium:524425
>
> Committed: https://crrev.com/a9441b0e7a2a56c2047482a3cc66e3ca2255444b
> Cr-Commit-Position: refs/heads/master@{#33695}
TBR=hpayer@chromium.org,mlippautz@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:524425
Review URL: https://codereview.chromium.org/1663013002
Cr-Commit-Position: refs/heads/master@{#33696}
Reason for revert:
Bug: failing to use write barrier when writing code entry into closure.
Original issue's description:
> Reland of Type Feedback Vector lives in the closure
>
> (Fixed a bug found by nosnap builds.)
>
> We get less "pollution" of type feedback if we have one vector per native
> context, rather than one for the whole system. This CL moves the vector
> appropriately.
>
> We rely more heavily on the Optimized Code Map in the SharedFunctionInfo. The
> vector actually lives in the first slot of the literals array (indeed there is
> great commonality between those arrays, they can be thought of as the same
> thing). So we make greater effort to ensure there is a valid literals array
> after compilation.
>
> This meant, for performance reasons, that we needed to extend
> FastNewClosureStub to support creating closures with literals. And ultimately,
> it drove us to move the optimized code map lookup out of FastNewClosureStub
> and into the compile lazy builtin.
>
> The heap change is trivial so I TBR Hannes for it...
>
> TBR=hpayer@chromium.org
> BUG=
>
> Committed: https://crrev.com/d984b3b0ce91e55800f5323b4bb32a06f8a5aab1
> Cr-Commit-Position: refs/heads/master@{#33548}
TBR=bmeurer@chromium.org,yangguo@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=
Review URL: https://codereview.chromium.org/1643533003
Cr-Commit-Position: refs/heads/master@{#33556}
This reverts commit 85ba94f28c.
All parallelism can be turned off using --predictable, or --noparallel-compaction.
This patch completely parallelizes
- semispace copy: from space -> to space (within newspace)
- newspace evacuation: newspace -> oldspace
- oldspace compaction: oldspace -> oldspace
Previously newspace has been handled sequentially (semispace copy, newspace
evacuation) before compacting oldspace in parallel. However, on a high level
there are no dependencies between those two actions, hence we parallelize them
altogether. We base the number of evacuation tasks on the overall set of
to-be-processed pages (newspace + oldspace compaction pages).
Some low-level details:
- The hard cap on number of tasks has been lifted
- We cache store buffer entries locally before merging them back into the global
StoreBuffer in a finalization phase.
- We cache AllocationSite operations locally before merging them back into the
global pretenuring storage in a finalization phase.
- AllocationSite might be compacted while they would be needed for newspace
evacuation. To mitigate any problems we defer checking allocation sites for
newspace till merging locally buffered data.
CQ_EXTRA_TRYBOTS=tryserver.v8:v8_linux_arm64_gc_stress_dbg,v8_linux_gc_stress_dbg,v8_mac_gc_stress_dbg,v8_linux64_asan_rel,v8_linux64_tsan_rel,v8_mac64_asan_rel
BUG=chromium:524425
LOG=N
R=hpayer@chromium.org, ulan@chromium.org
Review URL: https://codereview.chromium.org/1640563004
Cr-Commit-Position: refs/heads/master@{#33552}
(Fixed a bug found by nosnap builds.)
We get less "pollution" of type feedback if we have one vector per native
context, rather than one for the whole system. This CL moves the vector
appropriately.
We rely more heavily on the Optimized Code Map in the SharedFunctionInfo. The
vector actually lives in the first slot of the literals array (indeed there is
great commonality between those arrays, they can be thought of as the same
thing). So we make greater effort to ensure there is a valid literals array
after compilation.
This meant, for performance reasons, that we needed to extend
FastNewClosureStub to support creating closures with literals. And ultimately,
it drove us to move the optimized code map lookup out of FastNewClosureStub
and into the compile lazy builtin.
The heap change is trivial so I TBR Hannes for it...
TBR=hpayer@chromium.org
BUG=
Review URL: https://codereview.chromium.org/1642613002
Cr-Commit-Position: refs/heads/master@{#33548}
Reason for revert:
[Sheriff] Leads to crashes on all webrtc chromium testers, e.g.:
https://build.chromium.org/p/chromium.webrtc/builders/Mac%20Tester/builds/49664
Original issue's description:
> [heap] Parallel newspace evacuation, semispace copy, and compaction \o/
>
> All parallelism can be turned off using --predictable, or --noparallel-compaction.
>
> This patch completely parallelizes
> - semispace copy: from space -> to space (within newspace)
> - newspace evacuation: newspace -> oldspace
> - oldspace compaction: oldspace -> oldspace
>
> Previously newspace has been handled sequentially (semispace copy, newspace
> evacuation) before compacting oldspace in parallel. However, on a high level
> there are no dependencies between those two actions, hence we parallelize them
> altogether. We base the number of evacuation tasks on the overall set of
> to-be-processed pages (newspace + oldspace compaction pages).
>
> Some low-level details:
> - The hard cap on number of tasks has been lifted
> - We cache store buffer entries locally before merging them back into the global
> StoreBuffer in a finalization phase.
> - We cache AllocationSite operations locally before merging them back into the
> global pretenuring storage in a finalization phase.
> - AllocationSite might be compacted while they would be needed for newspace
> evacuation. To mitigate any problems we defer checking allocation sites for
> newspace till merging locally buffered data.
>
> CQ_EXTRA_TRYBOTS=tryserver.v8:v8_linux_arm64_gc_stress_dbg,v8_linux_gc_stress_dbg,v8_mac_gc_stress_dbg,v8_linux64_asan_rel,v8_linux64_tsan_rel,v8_mac64_asan_rel
> BUG=chromium:524425
> LOG=N
> R=hpayer@chromium.org, ulan@chromium.org
>
> Committed: https://crrev.com/8f0fd8c0370ae8c5aab56491b879d7e30c329062
> Cr-Commit-Position: refs/heads/master@{#33523}
TBR=hpayer@chromium.org,ulan@chromium.org,mlippautz@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:524425
Review URL: https://codereview.chromium.org/1643473002
Cr-Commit-Position: refs/heads/master@{#33539}
All parallelism can be turned off using --predictable, or --noparallel-compaction.
This patch completely parallelizes
- semispace copy: from space -> to space (within newspace)
- newspace evacuation: newspace -> oldspace
- oldspace compaction: oldspace -> oldspace
Previously newspace has been handled sequentially (semispace copy, newspace
evacuation) before compacting oldspace in parallel. However, on a high level
there are no dependencies between those two actions, hence we parallelize them
altogether. We base the number of evacuation tasks on the overall set of
to-be-processed pages (newspace + oldspace compaction pages).
Some low-level details:
- The hard cap on number of tasks has been lifted
- We cache store buffer entries locally before merging them back into the global
StoreBuffer in a finalization phase.
- We cache AllocationSite operations locally before merging them back into the
global pretenuring storage in a finalization phase.
- AllocationSite might be compacted while they would be needed for newspace
evacuation. To mitigate any problems we defer checking allocation sites for
newspace till merging locally buffered data.
CQ_EXTRA_TRYBOTS=tryserver.v8:v8_linux_arm64_gc_stress_dbg,v8_linux_gc_stress_dbg,v8_mac_gc_stress_dbg,v8_linux64_asan_rel,v8_linux64_tsan_rel,v8_mac64_asan_rel
BUG=chromium:524425
LOG=N
R=hpayer@chromium.org, ulan@chromium.org
Review URL: https://codereview.chromium.org/1577853007
Cr-Commit-Position: refs/heads/master@{#33523}
This replace HeapType with a dedicated class that implements just what we need for field type tracking. In the next CL, I plan to remove FieldType::Iterator because FieldType can iterate over at most one map.
The ultimate plan is to get rid of templates in types.(h|cc) and remove type-inl.h.
TBR=rossberg@chromium.org
Review URL: https://codereview.chromium.org/1636013002
Cr-Commit-Position: refs/heads/master@{#33521}
Reason for revert:
FAilure on win32 bot, need to investigate webkit failures.
Original issue's description:
> Type Feedback Vector lives in the closure
>
> We get less "pollution" of type feedback if we have one vector per native
> context, rather than one for the whole system. This CL moves the vector
> appropriately.
>
> We rely more heavily on the Optimized Code Map in the SharedFunctionInfo. The
> vector actually lives in the first slot of the literals array (indeed there is
> great commonality between those arrays, they can be thought of as the same
> thing). So we make greater effort to ensure there is a valid literals array
> after compilation.
>
> This meant, for performance reasons, that we needed to extend
> FastNewClosureStub to support creating closures with literals. And ultimately,
> it drove us to move the optimized code map lookup out of FastNewClosureStub
> and into the compile lazy builtin.
>
> The heap change is trivial so I TBR Hannes for it...
>
> TBR=hpayer@chromium.org
>
> BUG=
>
> Committed: https://crrev.com/a5200f7ed4d11c6b882fa667da7a1864226544b4
> Cr-Commit-Position: refs/heads/master@{#33518}
TBR=bmeurer@chromium.org,akos.palfi@imgtec.com
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=
Review URL: https://codereview.chromium.org/1632993003
Cr-Commit-Position: refs/heads/master@{#33520}
We get less "pollution" of type feedback if we have one vector per native
context, rather than one for the whole system. This CL moves the vector
appropriately.
We rely more heavily on the Optimized Code Map in the SharedFunctionInfo. The
vector actually lives in the first slot of the literals array (indeed there is
great commonality between those arrays, they can be thought of as the same
thing). So we make greater effort to ensure there is a valid literals array
after compilation.
This meant, for performance reasons, that we needed to extend
FastNewClosureStub to support creating closures with literals. And ultimately,
it drove us to move the optimized code map lookup out of FastNewClosureStub
and into the compile lazy builtin.
The heap change is trivial so I TBR Hannes for it...
TBR=hpayer@chromium.org
BUG=
Review URL: https://codereview.chromium.org/1563213002
Cr-Commit-Position: refs/heads/master@{#33518}
- Remove semispace target capacity: It's unused and adds some unneeded
complexity
- Enforcing decl order for SemiSpace
- Move forward declarations in spaces.h to top
- Add all members to default constructor
BUG=chromium:581076
LOG=N
Review URL: https://codereview.chromium.org/1631713002
Cr-Commit-Position: refs/heads/master@{#33515}
- Completely rely on the concurrent sweeping state for SweepingCompleted()
- Rename the state accordingly.
CQ_EXTRA_TRYBOTS=tryserver.v8:v8_linux_arm64_gc_stress_dbg,v8_linux_gc_stress_dbg,v8_mac_gc_stress_dbg,v8_linux64_asan_rel,v8_linux64_tsan_rel,v8_mac64_asan_rel
R=hpayer@chromium.org
Review URL: https://codereview.chromium.org/1614953002
Cr-Commit-Position: refs/heads/master@{#33490}
This solves a bug discovered with fast accessors, where a pre-age prologue
was written into a stub. Since StaticMarkingVisitor<.>::IsFlushable will
only flush Code::FUNCTION [1], we'll restrict GeneratePreagedPrologue to
functions, too, instead of adding a Code::STUB restriction.
Also, generalize api accessor test cases to --optimize-for-size.
Also, fix CompilationCacheCachingBehavior for --optimize-for-size.
[1] https://code.google.com/p/chromium/codesearch#chromium/src/v8/src/heap/objects-visiting-inl.h&l=629-632
R=epertoso
BUG=
Review URL: https://codereview.chromium.org/1580323003
Cr-Commit-Position: refs/heads/master@{#33291}
Use the same mechanism that is already available for Crankshaft to not
leak all kinds of things in TurboFan generated code. Long-term we will
support weakness in a better way, but for now, just use the
infrastructure that is already in place to avoid memory leaks via
TurboFan generated code.
R=jarin@chromium.org, ulan@chromium.org
Review URL: https://codereview.chromium.org/1555743003
Cr-Commit-Position: refs/heads/master@{#33073}
This CL prepare newspace evacuation for parallel execution wrt. to actual
allocations. The priority for allocations is:
* Try to allocate from LAB if objects are below kMaxLabObjectSize
* Allocate directly (synchronized) from newspace for larger objects.
* Fall back to old space allocation (which will be backed by a local compaction
space in future).
Semantical change: Previously we did fall back to regular new space promotion if
we are OOM in old space. With this CL we fall back to new space promotion, which
could fail because of fragmentation, again leading to an old space allocation
that finally bails into OOM.
Newspace evacuation is still single threaded and requires further changes to
allocation site tracking.
BUG=chromium:524425
LOG=N
Review URL: https://codereview.chromium.org/1487853002
Cr-Commit-Position: refs/heads/master@{#32970}
This is based on the Skia Implementation.
More on the project can be found here:
https://docs.google.com/a/chromium.org/document/d/1_4LAnInOB8tM_DLjptWiszRwa4qwiSsDzMkO4tU-Qes/edit#heading=h.p97rw6yt8o2j
The V8 Tracing platform will replace the isolate->event_logger().
But since the current embedders (namely chromium) currently use the isolate->event_logger, I made the default implementation (event-tracer) call into isolate->event_logger if an event_logger was set.
Once the embedders properly implement the interface (for example in chromium it would look like this: https://codereview.chromium.org/707273005/), the default implementation will be doing nothing.
Once the embedders side is fixed, we will change how V8 uses the tracing framework beyond the call from Logger:CallEventLogger. (which would also include a d8 implementation)
BUG=v8:4560
LOG=N
Review URL: https://codereview.chromium.org/988893003
Cr-Commit-Position: refs/heads/master@{#32959}
Introduce a new Apply builtin that forms a correct and optimizable
foundation for the Function.prototype.apply, Reflect.construct and
Reflect.apply builtins (which properly does the PrepareForTailCall
as required by the ES2015 spec).
The new Apply builtin avoids going to the runtime if it is safe to
just access the backing store elements of the argArray, i.e. if you
pass a JSArray with no holes, or an unmapped, unmodified sloppy or
strict arguments object.
mips/mips64 ports by Balazs Kilvady <balazs.kilvady@imgtec.com>
CQ_INCLUDE_TRYBOTS=tryserver.v8:v8_linux64_tsan_rel
BUG=v8:4413, v8:4430
LOG=n
R=yangguo@chromium.org
Committed: e4d2538911
Review URL: https://codereview.chromium.org/1523753002 .
Cr-Commit-Position: refs/heads/master@{#32929}
Reason for revert:
Breaks TSAN somewhow: http://build.chromium.org/p/client.v8/builders/V8%20Linux64%20TSAN/builds/7000
Original issue's description:
> [es6] Correct Function.prototype.apply, Reflect.construct and Reflect.apply.
>
> Introduce a new Apply builtin that forms a correct and optimizable
> foundation for the Function.prototype.apply, Reflect.construct and
> Reflect.apply builtins (which properly does the PrepareForTailCall
> as required by the ES2015 spec).
>
> The new Apply builtin avoids going to the runtime if it is safe to
> just access the backing store elements of the argArray, i.e. if you
> pass a JSArray with no holes, or an unmapped, unmodified sloppy or
> strict arguments object.
>
> mips/mips64 ports by Balazs Kilvady <balazs.kilvady@imgtec.com>
>
> CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_chromium_rel_ng;tryserver.blink:linux_blink_rel
> BUG=v8:4413, v8:4430
> LOG=n
> R=yangguo@chromium.org
>
> Committed: e4d2538911TBR=yangguo@chromium.org,paul.lind@imgtec.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=v8:4413, v8:4430
Review URL: https://codereview.chromium.org/1533803002 .
Cr-Commit-Position: refs/heads/master@{#32928}
Introduce a new Apply builtin that forms a correct and optimizable
foundation for the Function.prototype.apply, Reflect.construct and
Reflect.apply builtins (which properly does the PrepareForTailCall
as required by the ES2015 spec).
The new Apply builtin avoids going to the runtime if it is safe to
just access the backing store elements of the argArray, i.e. if you
pass a JSArray with no holes, or an unmapped, unmodified sloppy or
strict arguments object.
mips/mips64 ports by Balazs Kilvady <balazs.kilvady@imgtec.com>
CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_chromium_rel_ng;tryserver.blink:linux_blink_rel
BUG=v8:4413, v8:4430
LOG=n
R=yangguo@chromium.org
Review URL: https://codereview.chromium.org/1523753002 .
Cr-Commit-Position: refs/heads/master@{#32927}
Tests for
* aborting a full page.
* partially aborting a page.
* partially aborting a page with pointers between aborted pages.
* partially aborting a page with store buffer entries.
Also introduces force_oom() which prohibits a old space to
expand
BUG=chromium:524425
LOG=N
CQ_EXTRA_TRYBOTS=tryserver.v8:v8_linux_nosnap_rel,v8_linux_nosnap_dbg,v8_win_nosnap_shared_rel,v8_win_nosnap_shared_compile_rel
Review URL: https://codereview.chromium.org/1518803005
Cr-Commit-Position: refs/heads/master@{#32899}
Reason for revert:
Failing on Win 32bit nosnap:
https://chromegw.corp.google.com/i/client.v8/builders/V8%20Win32%20-%20nosnap%20-%20shared/builds/10602
Original issue's description:
> [cctest] Add tests for aborting compaction of pages
>
> Tests for
> * aborting a full page.
> * partially aborting a page.
> * partially aborting a page with pointers between aborted pages.
> * partially aborting a page with store buffer entries.
>
> Also introduces force_oom() which prohibits a old space to
> expand
>
> BUG=chromium:524425
> LOG=N
TBR=ulan@chromium.org,hpayer@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:524425
Review URL: https://codereview.chromium.org/1514603008
Cr-Commit-Position: refs/heads/master@{#32785}
Tests for
* aborting a full page.
* partially aborting a page.
* partially aborting a page with pointers between aborted pages.
* partially aborting a page with store buffer entries.
Also introduces ShouldForceOOM() which prohibits a PagedSpace from expanding.
Compaction spaces refer to the corresponding actual space.
BUG=chromium:524425
LOG=N
Review URL: https://codereview.chromium.org/1511933002
Cr-Commit-Position: refs/heads/master@{#32783}
Compaction of the array with maps happens lazily upon adding new maps.
BUG=
Review URL: https://codereview.chromium.org/1481953002
Cr-Commit-Position: refs/heads/master@{#32717}
