f2fs: compress: avoid duplicate counting of valid blocks when read compressed file

Since cluster is basic unit of compression, one cluster is compressed or
not, so we can calculate valid blocks only for first page in cluster,
the other pages just skip.
Signed-off-by: Fengnan Chang <changfengnan@vivo.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/data.c

@@ -2299,6 +2299,7 @@ static int f2fs_mpage_readpages(struct inode *inode,
 		.nr_rpages = 0,
 		.nr_cpages = 0,
 	};
+	pgoff_t nc_cluster_idx = NULL_CLUSTER;
 #endif
 	unsigned nr_pages = rac ? readahead_count(rac) : 1;
 	unsigned max_nr_pages = nr_pages;
@@ -2331,12 +2332,23 @@ static int f2fs_mpage_readpages(struct inode *inode,
 				if (ret)
 					goto set_error_page;
 			}
-			ret = f2fs_is_compressed_cluster(inode, page->index);
-			if (ret < 0)
-				goto set_error_page;
-			else if (!ret)
-				goto read_single_page;
+			if (cc.cluster_idx == NULL_CLUSTER) {
+				if (nc_cluster_idx ==
+					page->index >> cc.log_cluster_size) {
+					goto read_single_page;
+				}
+
+				ret = f2fs_is_compressed_cluster(inode, page->index);
+				if (ret < 0)
+					goto set_error_page;
+				else if (!ret) {
+					nc_cluster_idx =
+						page->index >> cc.log_cluster_size;
+					goto read_single_page;
+				}
 
+				nc_cluster_idx = NULL_CLUSTER;
+			}
 			ret = f2fs_init_compress_ctx(&cc);
 			if (ret)
 				goto set_error_page;