// allocMSpanLocked allocates an mspan object.
//
// h.lock must be held.
//
// allocMSpanLocked must be called on the system stack because
// its caller holds the heap lock. See mheap for details.
// Running on the system stack also ensures that we won't
// switch Ps during this function. See tryAllocMSpan for details.
//
//go:systemstack
func (h *mheap) allocMSpanLocked() *mspan {
	assertLockHeld(&h.lock)

	pp := getg().m.p.ptr()
	if pp == nil {
		// We don't have a p so just do the normal thing.
		return (*mspan)(h.spanalloc.alloc())
	}
	// Refill the cache if necessary.
	if pp.mspancache.len == 0 {
		const refillCount = len(pp.mspancache.buf) / 2
		for i := 0; i < refillCount; i++ {
			pp.mspancache.buf[i] = (*mspan)(h.spanalloc.alloc())
		}
		pp.mspancache.len = refillCount
	}
	// Pull off the last entry in the cache.
	s := pp.mspancache.buf[pp.mspancache.len-1]
	pp.mspancache.len--
	return s
}

func (h *mheap) allocMSpanLocked() *mspan {
	assertLockHeld(&h.lock)

	pp := getg().m.p.ptr()
	if pp == nil {
		// We don't have a p so just do the normal thing.
		return (*mspan)(h.spanalloc.alloc())
	}
	// Refill the cache if necessary.
	if pp.mspancache.len == 0 {
		const refillCount = len(pp.mspancache.buf)
		for i := 0; i < refillCount; i++ {
			pp.mspancache.buf[i] = (*mspan)(h.spanalloc.alloc())
		}
		pp.mspancache.len = refillCount
	}
	// Pull off the last entry in the cache.
	s := pp.mspancache.buf[pp.mspancache.len-1]
	pp.mspancache.len--
	return s
}

func (h *mheap) allocMSpanLocked() *mspan {
	assertLockHeld(&h.lock)

	pp := getg().m.p.ptr()
	if pp == nil {
		// We don't have a p so just do the normal thing.
		return (*mspan)(h.spanalloc.alloc())
	}
	// Refill the cache if necessary.
	if pp.mspancache.len == 0 {
		const refillCount = len(pp.mspancache.buf) / 2
		for i := 0; i < refillCount; i++ {
			pp.mspancache.buf[i] = (*mspan)(h.spanalloc.alloc())
		}
		pp.mspancache.len = refillCount
	}
	// Pull off the last entry in the cache.
	s := pp.mspancache.buf[pp.mspancache.len-1]
	pp.mspancache.len--
	return s
}