DLPX-88427 Fix self-contradictory comment in metaslab_alloc_dva_exit

The previous comment incorrectly implied that a live map entry means
failure and contained an unfinished correction ("resets ts=0... no,
it doesn't").  Reword to accurately describe the control flow: the
entry is present on both success and failure paths; only PT_REGS_RC
determines whether the failure metric is emitted.

Addresses review comment on PR #121.

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

Author: dbshah12

bpf/estat/metaslab-alloc.c

@@ -224,12 +224,11 @@ metaslab_alloc_dva_exit(struct pt_regs *ctx,
 		return (0);
 
 	/*
-	 * A live entry here means the overall DVA allocation failed (on
-	 * success, metaslab_group_alloc_exit resets ts=0... no, it doesn't —
-	 * it only resets vd_name and asize).  Emit an "allocation failures"
-	 * metric only when the return value indicates failure (non-zero).
-	 * psize is stored in data->size from metaslab_alloc_dva_entry since
-	 * kretprobe argument registers may be clobbered by function return.
+	 * A live entry exists on both success and failure paths; only the
+	 * return code determines whether to emit an "allocation failures"
+	 * metric (non-zero RC = failure).  psize is read from data->size
+	 * rather than the kretprobe argument registers, which may be
+	 * clobbered by the time the function returns.
 	 */
 	if (PT_REGS_RC(ctx) != 0) {
 		char name[] = "allocation failures";