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Fixed the CI failures: the 16GB literal did not compile on 32-bit targets (ARM/MIPS) — Go type-checks the dead branch too. The reservation size is now a constant derived from TargetBits ( |
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The heap reserved a flat 1GB of virtual address space, so any allocation approaching 1GB failed regardless of how much memory the system had. One example is a scrypt key derivation buffer with N=1<<20 and r=8. The reservation is virtual, so pages cost physical RAM only when first touched, and allocateHeap still halves its request if mmap refuses. 32-bit targets keep the 1GB reserve.
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Fixes #5760.
allocateHeap caps the heap at 1GB on every target, so with -gc=conservative or
-gc=precise any single allocation approaching 1GB fails with out of memory no
matter how much system RAM is free. The case that hit this was a 1GiB scrypt
key derivation buffer (N=1<<20, r=8) in the skycoin wallet, on a machine with
16GB free.
Reserve 16GB of virtual address space on 64-bit targets instead. The mmap is a
reservation, not a commitment. Pages cost physical memory only when first
touched, and the existing halve on failure loop still adapts when the map is
refused. 32-bit targets keep the 1GB cap. The growHeap comment already points
this way, in "If we run out of memory, we should consider increasing
heapMaxSize on 64-bit systems."
Verified on linux/amd64 with -gc=conservative. Before the change,
make([]byte, 1536<<20) gives a fatal out of memory error with 15GB free. After
it, the same allocation succeeds and is usable across the whole range.
One behavioral note. Under the blocks GC on 64-bit hosts the practical limit
becomes actual system memory, matching the boehm default and big Go, so true
exhaustion surfaces as OS memory pressure rather than a fatal error at an
arbitrary 1GB.