runtime: use searchIdx in scavengeOne

This is an optimization that prevents N^2 behavior within a chunk, but
was accidentally skipped. There should be no functional change as a
result of this CL.

Fixes #54892.

Change-Id: I861967a2268699fdc3464bd41bc56618b5628e6b
Reviewed-on: https://go-review.googlesource.com/c/go/+/429255
Auto-Submit: Michael Knyszek <[email protected]>
Reviewed-by: Keith Randall <[email protected]>
Reviewed-by: Keith Randall <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Michael Knyszek <[email protected]>

Author: mknyszek

src/runtime/mgcscavenge.go

@@ -718,7 +718,7 @@ func (p *pageAlloc) scavengeOne(ci chunkIdx, searchIdx uint, max uintptr) uintpt
 	if p.summary[len(p.summary)-1][ci].max() >= uint(minPages) {
 		// We only bother looking for a candidate if there at least
 		// minPages free pages at all.
-		base, npages := p.chunkOf(ci).findScavengeCandidate(pallocChunkPages-1, minPages, maxPages)
+		base, npages := p.chunkOf(ci).findScavengeCandidate(searchIdx, minPages, maxPages)
 
 		// If we found something, scavenge it and return!
 		if npages != 0 {