Make zdb -R scale less poorly

zdb -R with :d tries to use gzip decompression 9 times per size.
There's absolutely no reason for that, they're all the same
decompressor.

Reviewed-by: Brian Atkinson <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Rich Ercolani <[email protected]>
Closes #15726

Author: rincebrain

cmd/zdb/zdb.c

@@ -8506,6 +8506,14 @@ zdb_decompress_block(abd_t *pabd, void *buf, void *lbuf, uint64_t lsize,
 	*cfuncp++ = ZIO_COMPRESS_LZ4;
 	*cfuncp++ = ZIO_COMPRESS_LZJB;
 	mask |= ZIO_COMPRESS_MASK(LZ4) | ZIO_COMPRESS_MASK(LZJB);
+	/*
+	 * Every gzip level has the same decompressor, no need to
+	 * run it 9 times per bruteforce attempt.
+	 */
+	mask |= ZIO_COMPRESS_MASK(GZIP_2) | ZIO_COMPRESS_MASK(GZIP_3);
+	mask |= ZIO_COMPRESS_MASK(GZIP_4) | ZIO_COMPRESS_MASK(GZIP_5);
+	mask |= ZIO_COMPRESS_MASK(GZIP_6) | ZIO_COMPRESS_MASK(GZIP_7);
+	mask |= ZIO_COMPRESS_MASK(GZIP_8) | ZIO_COMPRESS_MASK(GZIP_9);
 	for (int c = 0; c < ZIO_COMPRESS_FUNCTIONS; c++)
 		if (((1ULL << c) & mask) == 0)
 			*cfuncp++ = c;