heap command

heap space

Displays the space information of the V8 Heap.

The heap of V8 adopts the Space + Page structure, several Pages form a Space, and several Spaces form the V8 heap.

According to the new and old generation and their uses, it is divided into multiple Spaces such as new (new generation), new_lo (new generation large object), old (old generation), lo (old generation large object), ro (read-only object). The size of the Page that is usually used to store small objects is 256K, and the Page that stores large objects contains only one object.

heap space
heap space [space_name]
- space_name : old, new, lo, map, code etc.

heap space is used to display the space space usage within the v8 heap, where Commit is the size of the commit and Max is the maximum used size.

(gdb) heap space
SPACE NAME          COMMIT        MAX
RO_SPACE      :     151552     262144
MAP_SPACE     :     528384     528384
CODE_SPACE    :     360448     360448
CODE_LO_SPACE :      49152      49152
OLD_SPACE     :    2781184    4616192
LO_SPACE      :     401408     401408
NEW_LO_SPACE  :          0          0
NEW_SPACE     :    1048576
 - from_space :          0
 - to_space   :    1048576
Total Committed    5320704

heap space new 显示 new space (新生代小对象) 的所有 pages。

(gdb) heap space new
    0x667900000 : size(262144), sweep(0), start(0x667900120)
 0x176d3ce00000 : size(262144), sweep(0), start(0x176d3ce00120)
 0x10d414980000 : size(262144), sweep(0), start(0x10d414980120)
 0x159131e80000 : size(262144), sweep(0), start(0x159131e80120)
Total 4 pages.

heap page

Displays all objects Brief of the specified Page.

Brief is a short string used to display objects on a single line, generally consisting of 2-3 parts. Such as <Type Info TagPointer> From left to right, the first part is the object type, the middle part may show important tips, and the rightmost part shows the object's Tagging Pointer.

<JsFunction setTimeout 0x37c04dfc74f9>

Description 0x37c04dfc74f9 is a JsFunction object named setTimeout.

heap page [page_address]
- page_address: V8 Page starting memory address

(gdb) heap page 0x3c0214e40000
0x3c0214e40120: <PropertyArray 0x3c0214e40120>
0x3c0214e40140: <FunctionContext 0x3c0214e40140>
0x3c0214e40168: <JsObject 0x3c0214e40168>
0x3c0214e40180: <PropertyArray 0x3c0214e40180>
0x3c0214e401a0: <FunctionContext 0x3c0214e401a0>
0x3c0214e401c8: <JsObject 0x3c0214e401c8>
0x3c0214e401e0: <PropertyArray 0x3c0214e401e0>
0x3c0214e40200: <FunctionContext 0x3c0214e40200>
0x3c0214e40228: <JsObject 0x3c0214e40228>
0x3c0214e40240: <PropertyArray 0x3c0214e40240>
0x3c0214e40260: <FunctionContext 0x3c0214e40260>
0x3c0214e40288: <JsObject 0x3c0214e40288>
0x3c0214e402a0: <PropertyArray 0x3c0214e402a0>
0x3c0214e402c0: <FunctionContext 0x3c0214e402c0>
0x3c0214e402e8: <JsObject 0x3c0214e402e8>
0x3c0214e40300: <PropertyArray 0x3c0214e40300>
0x3c0214e40320: <FunctionContext 0x3c0214e40320>
0x3c0214e40348: <JsObject 0x3c0214e40348>
0x3c0214e40360: <PropertyArray 0x3c0214e40360>
0x3c0214e40380: <FunctionContext 0x3c0214e40380>
0x3c0214e403a8: <JsObject 0x3c0214e403a8>
0x3c0214e403c0: <PropertyArray 0x3c0214e403c0>
0x3c0214e403e0: <FunctionContext 0x3c0214e403e0>
0x3c0214e40408: <JsObject 0x3c0214e40408>
0x3c0214e40420: <PropertyArray 0x3c0214e40420>
0x3c0214e40438: <FunctionContext 0x3c0214e40438>
...
0x3c0214e503b0: <DescriptorArray 0x3c0214e503b0>
0x3c0214e50440: <DescriptorArray 0x3c0214e50440>
0x3c0214e504d0: <DescriptorArray 0x3c0214e504d0>
0x3c0214e50530: <DescriptorArray 0x3c0214e50530>
0x3c0214e505c0: <DescriptorArray 0x3c0214e505c0>
0x3c0214e50650: <DescriptorArray 0x3c0214e50650>
0x3c0214e506e0: <DescriptorArray 0x3c0214e506e0>
0x3c0214e50770: <FreeSpace 0x3c0214e50770>
Total Cnt(1206)
DumpChunk() takes 0.136 second(s).

heap summary

The abstract specifies the objects of the Space, sorted by map, and sorted by quantity.

heap summary [space_name]
- space_name: new, old, lo, new_lo etc.

The headers follow Map, Count, Bytes, Type.

(gdb) heap sum old
0x2048032c0829:        1           24 JS_OBJECT_TYPE
0x2048032c0fc1:        1           24 JS_OBJECT_TYPE
0x2048032c1099:        1           24 JS_OBJECT_TYPE
0x2048032c1129:        1           24 JS_OBJECT_TYPE
0x2048032c11b9:        1           24 JS_OBJECT_TYPE
0x2048032c2719:        1           24 JS_OBJECT_TYPE
0x2048032c27a9:        1           24 JS_OBJECT_TYPE
0x2048032c2839:        1           24 JS_OBJECT_TYPE
0x2048032c2f89:        1           24 JS_OBJECT_TYPE
0x2048032c3019:        1           24 JS_OBJECT_TYPE
...
0x2048032c0c61:      487        50352 FUNCTION_CONTEXT_TYPE
0x0b6f27201469:      492        15744 CALL_HANDLER_INFO_TYPE
0x0b6f27200ec9:      497        18112 FEEDBACK_METADATA_TYPE
0x0b6f27200fe9:      519       103592 BYTECODE_ARRAY_TYPE
0x0b6f27204c19:      636        71232 FUNCTION_TEMPLATE_INFO_TYPE
0x0b6f272058c1:      646        20672 LOAD_HANDLER_TYPE
0x0b6f27200891:      701       123768 SCOPE_INFO_TYPE
0x0b6f27201979:      835        26720 CONS_ONE_BYTE_STRING_TYPE
0x0b6f27200729:      900       157952 FIXED_ARRAY_TYPE
0x0b6f27201421:      930        43808 PROPERTY_ARRAY_TYPE
0x0b6f272006e1:     1068        59336 BYTE_ARRAY_TYPE
0x0b6f27200241:     1239       197352 DESCRIPTOR_ARRAY_TYPE
0x0b6f272009f9:     1312        20992 FOREIGN_TYPE
0x2048032c0751:     1484        94976 JS_FUNCTION_TYPE
0x0b6f27201781:     1688        40512 UNCOMPILED_DATA_WITHOUT_PREPARSE_DATA_TYPE
0x2048032c03f1:     1843       103208 JS_FUNCTION_TYPE
0x0b6f272012b9:     2200        52800 FEEDBACK_CELL_TYPE
0x0b6f27200849:     2464       103056 ONE_BYTE_STRING_TYPE
0x0b6f272008d9:     3525       197400 SHARED_FUNCTION_INFO_TYPE
0x0b6f27200409:     6858       234808 ONE_BYTE_INTERNALIZED_STRING_TYPE
ShowMapSummary() takes 1.582 second(s).

heap find

Find references in the V8 heap.

heap find [space_name][tagging]
- space_name: new, old, lo, new_lo etc.
- tagging: Tagging Pointer of the target object

(gdb) heap find old 0x3c0214e4c391
<FixedArray 0x3c0214e49e69>
find 1
(gdb) heap find old 0x3c0214e49e69
<JsArray 0xe953ab26d1>
find 1
(gdb) heap find old 0xe953ab26d1
<JsObject 0xe953ab2389>
find 1

heap snapshot

Export Heap Snapshots.

heap snapshot [filename]
- The default filename is core.heapsnapshot.

If you specify filename, make sure the suffix is heapsnapshot, otherwise it will not be recognized by DevTool.

(gdb) heap snap
Synchronize: (Strong roots)
Synchronize: (Bootstrapper)
Synchronize: (Relocatable)
Synchronize: (Debugger)
Synchronize: (Compilation cache)
Synchronize: (Builtins)
Synchronize: (Thread manager)
OnStackTracedNodeSpace.Iterate NotImplemented.
Synchronize: (Global handles)
Synchronize: (Stack roots)
Synchronize: (Handle scope)
Synchronize: (Eternal handles)
Synchronize: (Startup object cache)
Synchronize: (Internalized strings)
Synchronize: (External strings)
Iterated 1732 RO Heap Objects
failed RO Heap Object: 0
(enum v8::internal::AllocationSpace) v8::internal::RO_SPACE
(enum v8::internal::AllocationSpace) v8::internal::MAP_SPACE
(enum v8::internal::AllocationSpace) v8::internal::CODE_SPACE
(enum v8::internal::AllocationSpace) v8::internal::CODE_LO_SPACE
(enum v8::internal::AllocationSpace) v8::internal::OLD_SPACE
19.3%: 999.8/sec, Object(10000), Entry(34920), Edge(91684)
(enum v8::internal::AllocationSpace) v8::internal::LO_SPACE
(enum v8::internal::AllocationSpace) v8::internal::NEW_LO_SPACE
(enum v8::internal::AllocationSpace) v8::internal::NEW_SPACE
Iterated 43904 Objects
failed HeapObject: 0
heap snapshot written to 'core.heapsnapshot'
Generate() takes 14.629 second(s).

It takes more time when there are many objects, which can take up to several hours depending on the number of nodes and edges.

heap command

heap space​

heap page​

heap summary​

heap find​

heap snapshot​

heap space

heap page

heap summary

heap find

heap snapshot