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runtime: allow GOMEMLIMIT to parse non integer values with a suffix like 1.5GiB → 1536MiB #76923

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runtime: allow GOMEMLIMIT to parse non integer values with a suffix like 1.5GiB → 1536MiB#76923
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FeatureRequestIssues asking for a new feature that does not need a proposal.LibraryProposalIssues describing a requested change to the Go standard library or x/ libraries, but not to a toolNeedsDecisionFeedback is required from experts, contributors, and/or the community before a change can be made.compiler/runtimeIssues related to the Go compiler and/or runtime.
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@subnix

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@subnix
subnix
opened on Dec 19, 2025

Go version

go version go1.25.5 darwin/arm64

Output of go env in your module/workspace:

AR='ar'
CC='cc'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='c++'
GCCGO='gccgo'
GO111MODULE=''
GOARCH='arm64'
GOARM64='v8.0'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/Users/user/Library/Caches/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/Users/user/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/w4/9h406zs53_d82t0jx555j4ww0000gn/T/go-build2324368129=/tmp/go-build -gno-record-gcc-switches -fno-common'
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMOD='/tmp/testgo/go.mod'
GOMODCACHE='/Users/user/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Users/user/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/opt/homebrew/Cellar/go/1.25.5/libexec'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/Users/user/Library/Application Support/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/opt/homebrew/Cellar/go/1.25.5/libexec/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.25.5'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

GOMEMLIMIT=1.5GiB go run .

What did you see happen?

GOMEMLIMIT=1.5GiB
fatal error: malformed GOMEMLIMIT; see `go doc runtime/debug.SetMemoryLimit`

runtime stack:
runtime.throw({0x10337f090?, 0xa?})
	runtime/panic.go:1094 +0x34 fp=0x16d03eeb0 sp=0x16d03ee80 pc=0x102e367d4
runtime.readGOMEMLIMIT()
	runtime/mgcpacer.go:1365 +0xb4 fp=0x16d03eee0 sp=0x16d03eeb0 pc=0x102de9c14
runtime.gcinit()
	runtime/mgc.go:189 +0x38 fp=0x16d03ef10 sp=0x16d03eee0 pc=0x102de0318
runtime.schedinit()
	runtime/proc.go:898 +0x1c0 fp=0x16d03ef80 sp=0x16d03ef10 pc=0x102e02b70
runtime.rt0_go()
	runtime/asm_arm64.s:121 +0xcc fp=0x16d03efb0 sp=0x16d03ef80 pc=0x102e3c6dc

What did you expect to see?

According to the documentation GOMEMLIMIT is a numeric value with an optional unit suffix:

go/src/runtime/extern.go

Lines 27 to 33 in d00e96d

program. GOMEMLIMIT is a numeric value in bytes with an optional unit suffix.
The supported suffixes include B, KiB, MiB, GiB, and TiB. These suffixes
represent quantities of bytes as defined by the IEC 80000-13 standard. That is,
they are based on powers of two: KiB means 2^10 bytes, MiB means 2^20 bytes,
and so on. The default setting is [math.MaxInt64], which effectively disables the
memory limit. [runtime/debug.SetMemoryLimit] allows changing this limit at run
time.

And numeric types include:

go/doc/go_spec.html

Lines 841 to 846 in d00e96d

<h3 id="Numeric_types">Numeric types</h3>
<p>
An <i>integer</i>, <i>floating-point</i>, or <i>complex</i> type
represents the set of integer, floating-point, or complex values, respectively.
They are collectively called <i>numeric types</i>.

However, GOMEMLIMIT only accepts integers:

go/src/runtime/string.go

Lines 402 to 415 in d00e96d

// parseByteCount parses a string that represents a count of bytes.
//
// s must match the following regular expression:
//
// ^[0-9]+(([KMGT]i)?B)?$
//
// In other words, an integer byte count with an optional unit
// suffix. Acceptable suffixes include one of
// - KiB, MiB, GiB, TiB which represent binary IEC/ISO 80000 units, or
// - B, which just represents bytes.
//
// Returns an int64 because that's what its callers want and receive,
// but the result is always non-negative.
func parseByteCount(s string) (int64, bool) {

Therefore, I would expect GOMEMLIMIT to either accept a float value or explicitly specify the types it accepts. For instance, systemd allows specifying memory constraints using a float value with a suffix.

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