f2fs: compress: fix overwrite may reduce compress ratio unproperly

when overwrite only first block of cluster, since cluster is not full, it
will call f2fs_write_raw_pages when f2fs_write_multi_pages, and cause the
whole cluster become uncompressed eventhough data can be compressed.
this may will make random write bench score reduce a lot.

root# dd if=/dev/zero of=./fio-test bs=1M count=1

root# sync

root# echo 3 > /proc/sys/vm/drop_caches

root# f2fs_io get_cblocks ./fio-test

root# dd if=/dev/zero of=./fio-test bs=4K count=1 oflag=direct conv=notrunc

w/o patch:
root# f2fs_io get_cblocks ./fio-test
189

w/ patch:
root# f2fs_io get_cblocks ./fio-test
192
Signed-off-by: Fengnan Chang <changfengnan@vivo.com>
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/compress.c

@@ -881,6 +881,25 @@ bool f2fs_cluster_can_merge_page(struct compress_ctx *cc, pgoff_t index)
 	return is_page_in_cluster(cc, index);
 }
 
+bool f2fs_all_cluster_page_loaded(struct compress_ctx *cc, struct pagevec *pvec,
+				int index, int nr_pages)
+{
+	unsigned long pgidx;
+	int i;
+
+	if (nr_pages - index < cc->cluster_size)
+		return false;
+
+	pgidx = pvec->pages[index]->index;
+
+	for (i = 1; i < cc->cluster_size; i++) {
+		if (pvec->pages[index + i]->index != pgidx + i)
+			return false;
+	}
+
+	return true;
+}
+
 static bool cluster_has_invalid_data(struct compress_ctx *cc)
 {
 	loff_t i_size = i_size_read(cc->inode);

fs/f2fs/data.c

@@ -3040,6 +3040,10 @@ static int f2fs_write_cache_pages(struct address_space *mapping,
 			need_readd = false;
 #ifdef CONFIG_F2FS_FS_COMPRESSION
 			if (f2fs_compressed_file(inode)) {
+				void *fsdata = NULL;
+				struct page *pagep;
+				int ret2;
+
 				ret = f2fs_init_compress_ctx(&cc);
 				if (ret) {
 					done = 1;
@@ -3058,27 +3062,23 @@ static int f2fs_write_cache_pages(struct address_space *mapping,
 				if (unlikely(f2fs_cp_error(sbi)))
 					goto lock_page;
 
-				if (f2fs_cluster_is_empty(&cc)) {
-					void *fsdata = NULL;
-					struct page *pagep;
-					int ret2;
+				if (!f2fs_cluster_is_empty(&cc))
+					goto lock_page;
 
-					ret2 = f2fs_prepare_compress_overwrite(
+				ret2 = f2fs_prepare_compress_overwrite(
 							inode, &pagep,
 							page->index, &fsdata);
-					if (ret2 < 0) {
-						ret = ret2;
-						done = 1;
-						break;
-					} else if (ret2 &&
-						!f2fs_compress_write_end(inode,
-								fsdata, page->index,
-								1)) {
-						retry = 1;
-						break;
-					}
-				} else {
-					goto lock_page;
+				if (ret2 < 0) {
+					ret = ret2;
+					done = 1;
+					break;
+				} else if (ret2 &&
+					(!f2fs_compress_write_end(inode,
+						fsdata, page->index, 1) ||
+					 !f2fs_all_cluster_page_loaded(&cc,
+						&pvec, i, nr_pages))) {
+					retry = 1;
+					break;
 				}
 			}
 #endif

fs/f2fs/f2fs.h

@@ -4052,6 +4052,8 @@ void f2fs_end_read_compressed_page(struct page *page, bool failed,
 							block_t blkaddr);
 bool f2fs_cluster_is_empty(struct compress_ctx *cc);
 bool f2fs_cluster_can_merge_page(struct compress_ctx *cc, pgoff_t index);
+bool f2fs_all_cluster_page_loaded(struct compress_ctx *cc, struct pagevec *pvec,
+				int index, int nr_pages);
 bool f2fs_sanity_check_cluster(struct dnode_of_data *dn);
 void f2fs_compress_ctx_add_page(struct compress_ctx *cc, struct page *page);
 int f2fs_write_multi_pages(struct compress_ctx *cc,