// Clear the second allocCount just to be safe.
		s.allocCountBeforeCache = 0
	}

	// Get a new cached span from the central lists.
	s = mheap_.central[spc].mcentral.cacheSpan()
	if s == nil {
		throw("out of memory")
	}

	if s.allocCount == s.nelems {
		throw("span has no free space")
	}

	// Indicate that this span is cached and prevent asynchronous

//
// * The object reclaimer finds and frees unmarked slots in spans. It
//   can free a whole span if none of the objects are marked, but that
//   isn't its goal. This can be driven either synchronously by
//   mcentral.cacheSpan for mcentral spans, or asynchronously by
//   sweepone, which looks at all the mcentral lists.
//
// * The span reclaimer looks for spans that contain no marked objects