From 3968a5bca4fc0cdb4e2bb9fd6169deafdafc420d Mon Sep 17 00:00:00 2001 From: Russ Cox Date: Tue, 4 Mar 2025 10:31:02 -0500 Subject: runtime: handle m0 padding better The SpinbitMutex experiment requires m structs other than m0 to be allocated in 2048-byte size class, by adding padding. Do the calculation more explicitly, to avoid future CLs like CL 653335. Change-Id: I83ae1e86ef3711ab65441f4e487f94b9e1429029 Reviewed-on: https://go-review.googlesource.com/c/go/+/654595 Reviewed-by: Rhys Hiltner Reviewed-by: Michael Knyszek LUCI-TryBot-Result: Go LUCI Auto-Submit: Michael Knyszek --- src/runtime/runtime2.go | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) (limited to 'src/runtime/runtime2.go') diff --git a/src/runtime/runtime2.go b/src/runtime/runtime2.go index 6b9f49d503..4318930d9c 100644 --- a/src/runtime/runtime2.go +++ b/src/runtime/runtime2.go @@ -619,13 +619,18 @@ type m struct { // Up to 10 locks held by this m, maintained by the lock ranking code. locksHeldLen int locksHeld [10]heldLockInfo +} + +const mRedZoneSize = (16 << 3) * asanenabledBit // redZoneSize(2048) + +type mPadded struct { + m // Size the runtime.m structure so it fits in the 2048-byte size class, and // not in the next-smallest (1792-byte) size class. That leaves the 11 low // bits of muintptr values available for flags, as required for // GOEXPERIMENT=spinbitmutex. - _ [goexperiment.SpinbitMutexInt * 64 * goarch.PtrSize / 8]byte - _ [goexperiment.SpinbitMutexInt * 700 * (2 - goarch.PtrSize/4)]byte + _ [goexperiment.SpinbitMutexInt * (2048 - mallocHeaderSize - mRedZoneSize - unsafe.Sizeof(m{}))]byte } type p struct { -- cgit v1.3