Disable pointer compression? Disable the sandbox?

[Ben Ernst]

Hey team.

I've been following the conversations around pointer compression and the memory usage caps that this feature imposes on v8. I compile my own V8 to use in an embedded context. What is the current state of affairs of memory limits in V8, and to what extent can I disable, increase, or workaround them? What GN compile-time flags should I be setting? I'm currently on V8 11.6. I target only Windows 10+ and Ubuntu 18.04+. I used to set run-time flag "--max-old-space-size" but that doesn't seem to do what it used to do.

My existing compile flags are as follows:

treat_warnings_as_errors=false
v8_enable_i18n_support=false
v8_monolithic=true
is_component_build=false
use_custom_libcxx=false
is_clang=false
v8_use_external_startup_data=false

Thanks in advance!

Ben

[Jakob Kummerow]

With the default configuration, --max-old-space-size should work for values up to 4GiB.

If you need more, you need to disable pointer compression (which implies disabling the sandbox, because the sandbox relies on compressed pointers for its isolation mechanics). That's easy to do with:

v8_enable_pointer_compression = false

v8_enable_sandbox = false

Note that this will increase memory consumption by probably around 60-70% (pointers become twice as big, non-pointer data such as numbers and string characters remains the same, so the overall balance depends on your workload). 

This will allow you to configure arbitrary maximum heap sizes.

Note that you need to #define (or not define) V8_COMPRESS_POINTERS for the parts of your embedding code that #include V8 headers such that it matches your V8 build configuration.

[Ben Ernst]

Thank you very much Jakob, that's precisely the guidance that I was looking for.

Warm regards,

Ben

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