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doc: correct definition of v8.getHeapStatistics().heap_size_limit #57029

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doc: correct definition of v8.getHeapStatistics().heap_size_limit #57029

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cf85d63
typo
inwenis Feb 13, 2025
bd02709
fix heap docs
inwenis Feb 13, 2025
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3 changes: 2 additions & 1 deletion doc/api/v8.md
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Expand Up @@ -219,7 +219,8 @@ does not include memory that has been allocated but not yet used.

`heap_size_limit` The value of heap\_size\_limit is the maximum size of the V8
heap, in bytes (either the default limit, determined by system resources, or
the value passed to the `--max_old_space_size` option).
the value passed to the `--max-old-space-size` option plus heap's semi space plus
heap's young generation space).
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The semi space and young generation space are referring to the same concept. I think a more straightforward hint here will be pointing to --max-heap-size:

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the value passed to the `--max-old-space-size` option plus heap's semi space plus
heap's young generation space).
the value passed to the `--max-heap-size` option).

Though, both --max_semi_space_size and --max_old_space_size take precedence over --max-heap-size option, and are hinted via node --v8-options.

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https://nodejs.org/api/cli.html does not describe --max-heap-size.

The semi space and young generation space are referring to the same concept - I agree
But the docs below say heap=old-space + semi-space + 3*semi-space (young generation) however my tests showed that this math doesn't hold up with reality.
https://nodejs.org/api/cli.html#--max-semi-space-sizesize-in-mib

I would love for the docs to be exhaustive and non ambiguous.
It seemed to me that the least ambiguous definition of the heap size is the sum of its "parts".

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That document refers to the large new object space, whose size is implied with the --max-semi-space-size, is also counted in the formula: https://source.chromium.org/chromium/chromium/src/+/main:v8/src/heap/heap.cc;l=203-208?q=Heap::MaxReserved

There are many factors in V8 that can change the assumed formula of the heap limit size, like the conditions in the link above. Given that these flags are maintained in V8, rather than node, I'd still suggest refer to --max-heap-size, which is the most striaghtforward to set the general limit.


`malloced_memory` The value of malloced\_memory is the number of bytes allocated
through `malloc` by V8.
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