executor: reduce zlib memory consumption

The images we unpack has huge ranges of 0s.
Currently we write all bytes and as the result page in whole unpacked image.
Don't write 0s since we just mmaped zero memory.
This reduces btrfs_0 seed memory consumption from 130MB to 6MB.

1 files changed, 8 insertions, 5 deletions

diff --git a/executor/common_zlib.h b/executor/common_zlib.h
index 5f8124318..24382ac0c 100644
--- a/executor/common_zlib.h
+++ b/executor/common_zlib.h
@@ -98,8 +98,10 @@ static int puff_stored(struct puff_state* s)
 		return 2; // not enough input
 	if (s->outcnt + len > s->outlen)
 		return 1; // not enough output space
-	while (len--)
-		s->out[s->outcnt++] = s->in[s->incnt++];
+	for (; len--; s->outcnt++, s->incnt++) {
+		if (s->in[s->incnt])
+			s->out[s->outcnt] = s->in[s->incnt];
+	}
 
 	// done with a valid stored block
 	return 0;
@@ -243,7 +245,8 @@ static int puff_codes(struct puff_state* s,
 			// write out the literal
 			if (s->outcnt == s->outlen)
 				return 1;
-			s->out[s->outcnt] = symbol;
+			if (symbol)
+				s->out[s->outcnt] = symbol;
 			s->outcnt++;
 		} else if (symbol > 256) { // length
 			// get and compute length
@@ -264,8 +267,8 @@ static int puff_codes(struct puff_state* s,
 			if (s->outcnt + len > s->outlen)
 				return 1;
 			while (len--) {
-				s->out[s->outcnt] =
-				    dist > s->outcnt ? 0 : s->out[s->outcnt - dist];
+				if (dist <= s->outcnt && s->out[s->outcnt - dist])
+					s->out[s->outcnt] = s->out[s->outcnt - dist];
 				s->outcnt++;
 			}
 		}