erofs: enable sub-page compressed block support

Let's just disable cached decompression and inplace I/Os for partial
pages as the first step in order to enable sub-page block initial
support.  In other words, currently it works primarily based on
temporary short-lived pages.  Don't expect too much in terms of
performance.
Reviewed-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20231206091057.87027-6-hsiangkao@linux.alibaba.com

fs/erofs/inode.c

@@ -259,8 +259,10 @@ static int erofs_fill_inode(struct inode *inode)
 
 	if (erofs_inode_is_data_compressed(vi->datalayout)) {
 #ifdef CONFIG_EROFS_FS_ZIP
-		if (!erofs_is_fscache_mode(inode->i_sb) &&
-		    inode->i_sb->s_blocksize_bits == PAGE_SHIFT) {
+		if (!erofs_is_fscache_mode(inode->i_sb)) {
+			DO_ONCE_LITE_IF(inode->i_sb->s_blocksize != PAGE_SIZE,
+				  erofs_info, inode->i_sb,
+				  "EXPERIMENTAL EROFS subpage compressed block support in use. Use at your own risk!");
 			inode->i_mapping->a_ops = &z_erofs_aops;
 			err = 0;
 			goto out_unlock;

fs/erofs/zdata.c

@@ -563,6 +563,8 @@ static void z_erofs_bind_cache(struct z_erofs_decompress_frontend *fe)
 			__GFP_NOMEMALLOC | __GFP_NORETRY | __GFP_NOWARN;
 	unsigned int i;
 
+	if (i_blocksize(fe->inode) != PAGE_SIZE)
+		return;
 	if (fe->mode < Z_EROFS_PCLUSTER_FOLLOWED)
 		return;
 
@@ -967,12 +969,12 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
 	struct inode *const inode = fe->inode;
 	struct erofs_map_blocks *const map = &fe->map;
 	const loff_t offset = page_offset(page);
+	const unsigned int bs = i_blocksize(inode);
 	bool tight = true, exclusive;
 	unsigned int cur, end, len, split;
 	int err = 0;
 
 	z_erofs_onlinepage_init(page);
-
 	split = 0;
 	end = PAGE_SIZE;
 repeat:
@@ -1021,7 +1023,7 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
 	 * for inplace I/O or bvpage (should be processed in a strict order.)
 	 */
 	tight &= (fe->mode > Z_EROFS_PCLUSTER_FOLLOWED_NOINPLACE);
-	exclusive = (!cur && ((split <= 1) || tight));
+	exclusive = (!cur && ((split <= 1) || (tight && bs == PAGE_SIZE)));
 	if (cur)
 		tight &= (fe->mode >= Z_EROFS_PCLUSTER_FOLLOWED);