Merge tag 'erofs-for-5.19-rc1-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs

Pull more erofs updates from Gao Xiang:
 "This is a follow-up to the main updates, including some fixes of
  fscache mode related to compressed inodes and a cachefiles tracepoint.
  There is also a patch to fix an unexpected decompression strategy
  change due to a cleanup in the past. All the fixes are quite small.

  Apart from these, documentation is also updated for a better
  description of recent new features.

  In addition, this has some trivial cleanups without actual code logic
  changes, so I could have a more recent codebase to work on folios and
  avoiding the PG_error page flag for the next cycle.

  Summary:

   - Leave compressed inodes unsupported in fscache mode for now

   - Avoid crash when using tracepoint cachefiles_prep_read

   - Fix `backmost' behavior due to a recent cleanup

   - Update documentation for better description of recent new features

   - Several decompression cleanups w/o logical change"

* tag 'erofs-for-5.19-rc1-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs:
  erofs: fix 'backmost' member of z_erofs_decompress_frontend
  erofs: simplify z_erofs_pcluster_readmore()
  erofs: get rid of label `restart_now'
  erofs: get rid of `struct z_erofs_collection'
  erofs: update documentation
  erofs: fix crash when enable tracepoint cachefiles_prep_read
  erofs: leave compressed inodes unsupported in fscache mode for now

5 files changed, 136 insertions, 151 deletions

diff --git a/Documentation/filesystems/erofs.rst b/Documentation/filesystems/erofs.rst
index bef6d3040ce4..05e03d54af1a 100644
--- a/Documentation/filesystems/erofs.rst
+++ b/Documentation/filesystems/erofs.rst
@@ -1,63 +1,82 @@
 .. SPDX-License-Identifier: GPL-2.0
 
 ======================================
-Enhanced Read-Only File System - EROFS
+EROFS - Enhanced Read-Only File System
 ======================================
 
 Overview
 ========
 
-EROFS file-system stands for Enhanced Read-Only File System. Different
-from other read-only file systems, it aims to be designed for flexibility,
-scalability, but be kept simple and high performance.
+EROFS filesystem stands for Enhanced Read-Only File System.  It aims to form a
+generic read-only filesystem solution for various read-only use cases instead
+of just focusing on storage space saving without considering any side effects
+of runtime performance.
 
-It is designed as a better filesystem solution for the following scenarios:
+It is designed to meet the needs of flexibility, feature extendability and user
+payload friendly, etc.  Apart from those, it is still kept as a simple
+random-access friendly high-performance filesystem to get rid of unneeded I/O
+amplification and memory-resident overhead compared to similar approaches.
+
+It is implemented to be a better choice for the following scenarios:
 
  - read-only storage media or
 
  - part of a fully trusted read-only solution, which means it needs to be
    immutable and bit-for-bit identical to the official golden image for
-   their releases due to security and other considerations and
+   their releases due to security or other considerations and
 
  - hope to minimize extra storage space with guaranteed end-to-end performance
    by using compact layout, transparent file compression and direct access,
    especially for those embedded devices with limited memory and high-density
-   hosts with numerous containers;
+   hosts with numerous containers.
 
 Here is the main features of EROFS:
 
  - Little endian on-disk design;
 
- - Currently 4KB block size (nobh) and therefore maximum 16TB address space;
-
- - Metadata & data could be mixed by design;
+ - 4KiB block size and 32-bit block addresses, therefore 16TiB address space
+   at most for now;
 
- - 2 inode versions for different requirements:
+ - Two inode layouts for different requirements:
 
-   =====================  ============  =====================================
+   =====================  ============  ======================================
                           compact (v1)  extended (v2)
-   =====================  ============  =====================================
+   =====================  ============  ======================================
    Inode metadata size    32 bytes      64 bytes
-   Max file size          4 GB          16 EB (also limited by max. vol size)
+   Max file size          4 GiB         16 EiB (also limited by max. vol size)
    Max uids/gids          65536         4294967296
    Per-inode timestamp    no            yes (64 + 32-bit timestamp)
    Max hardlinks          65536         4294967296
-   Metadata reserved      4 bytes       14 bytes
-   =====================  ============  =====================================
+   Metadata reserved      8 bytes       18 bytes
+   =====================  ============  ======================================
+
+ - Metadata and data could be mixed as an option;
 
  - Support extended attributes (xattrs) as an option;
 
- - Support xattr inline and tail-end data inline for all files;
+ - Support tailpacking data and xattr inline compared to byte-addressed
+   unaligned metadata or smaller block size alternatives;
 
  - Support POSIX.1e ACLs by using xattrs;
 
  - Support transparent data compression as an option:
-   LZ4 algorithm with the fixed-sized output compression for high performance;
+   LZ4 and MicroLZMA algorithms can be used on a per-file basis; In addition,
+   inplace decompression is also supported to avoid bounce compressed buffers
+   and page cache thrashing.
+
+ - Support direct I/O on uncompressed files to avoid double caching for loop
+   devices;
 
- - Multiple device support for multi-layer container images.
+ - Support FSDAX on uncompressed images for secure containers and ramdisks in
+   order to get rid of unnecessary page cache.
+
+ - Support multiple devices for multi blob container images;
+
+ - Support file-based on-demand loading with the Fscache infrastructure.
 
 The following git tree provides the file system user-space tools under
-development (ex, formatting tool mkfs.erofs):
+development, such as a formatting tool (mkfs.erofs), an on-disk consistency &
+compatibility checking tool (fsck.erofs), and a debugging tool (dump.erofs):
 
 - git://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs-utils.git
 
@@ -91,6 +110,7 @@ dax={always,never}     Use direct access (no page cache).  See
                        Documentation/filesystems/dax.rst.
 dax                    A legacy option which is an alias for ``dax=always``.
 device=%s              Specify a path to an extra device to be used together.
+fsid=%s                Specify a filesystem image ID for Fscache back-end.
 ===================    =========================================================
 
 Sysfs Entries
@@ -226,8 +246,8 @@ Note that apart from the offset of the first filename, nameoff0 also indicates
 the total number of directory entries in this block since it is no need to
 introduce another on-disk field at all.
 
-Chunk-based file
-----------------
+Chunk-based files
+-----------------
 In order to support chunk-based data deduplication, a new inode data layout has
 been supported since Linux v5.15: Files are split in equal-sized data chunks
 with ``extents`` area of the inode metadata indicating how to get the chunk
diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
index a5cc4ed2cd0d..8e01d89c3319 100644
--- a/fs/erofs/fscache.c
+++ b/fs/erofs/fscache.c
@@ -17,6 +17,7 @@ static struct netfs_io_request *erofs_fscache_alloc_request(struct address_space
 	rreq->start	= start;
 	rreq->len	= len;
 	rreq->mapping	= mapping;
+	rreq->inode	= mapping->host;
 	INIT_LIST_HEAD(&rreq->subrequests);
 	refcount_set(&rreq->ref, 1);
 	return rreq;
diff --git a/fs/erofs/inode.c b/fs/erofs/inode.c
index bcc8335b46b3..95a403720e8c 100644
--- a/fs/erofs/inode.c
+++ b/fs/erofs/inode.c
@@ -288,7 +288,10 @@ static int erofs_fill_inode(struct inode *inode, int isdir)
 	}
 
 	if (erofs_inode_is_data_compressed(vi->datalayout)) {
-		err = z_erofs_fill_inode(inode);
+		if (!erofs_is_fscache_mode(inode->i_sb))
+			err = z_erofs_fill_inode(inode);
+		else
+			err = -EOPNOTSUPP;
 		goto out_unlock;
 	}
 	inode->i_mapping->a_ops = &erofs_raw_access_aops;
diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index 95efc127b2ba..724bb57075f6 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -199,7 +199,6 @@ struct z_erofs_decompress_frontend {
 	struct z_erofs_pagevec_ctor vector;
 
 	struct z_erofs_pcluster *pcl, *tailpcl;
-	struct z_erofs_collection *cl;
 	/* a pointer used to pick up inplace I/O pages */
 	struct page **icpage_ptr;
 	z_erofs_next_pcluster_t owned_head;
@@ -214,7 +213,7 @@ struct z_erofs_decompress_frontend {
 
 #define DECOMPRESS_FRONTEND_INIT(__i) { \
 	.inode = __i, .owned_head = Z_EROFS_PCLUSTER_TAIL, \
-	.mode = COLLECT_PRIMARY_FOLLOWED }
+	.mode = COLLECT_PRIMARY_FOLLOWED, .backmost = true }
 
 static struct page *z_pagemap_global[Z_EROFS_VMAP_GLOBAL_PAGES];
 static DEFINE_MUTEX(z_pagemap_global_lock);
@@ -357,7 +356,7 @@ static bool z_erofs_try_inplace_io(struct z_erofs_decompress_frontend *fe,
 	return false;
 }
 
-/* callers must be with collection lock held */
+/* callers must be with pcluster lock held */
 static int z_erofs_attach_page(struct z_erofs_decompress_frontend *fe,
 			       struct page *page, enum z_erofs_page_type type,
 			       bool pvec_safereuse)
@@ -372,7 +371,7 @@ static int z_erofs_attach_page(struct z_erofs_decompress_frontend *fe,
 
 	ret = z_erofs_pagevec_enqueue(&fe->vector, page, type,
 				      pvec_safereuse);
-	fe->cl->vcnt += (unsigned int)ret;
+	fe->pcl->vcnt += (unsigned int)ret;
 	return ret ? 0 : -EAGAIN;
 }
 
@@ -405,12 +404,11 @@ static void z_erofs_try_to_claim_pcluster(struct z_erofs_decompress_frontend *f)
 	f->mode = COLLECT_PRIMARY;
 }
 
-static int z_erofs_lookup_collection(struct z_erofs_decompress_frontend *fe,
-				     struct inode *inode,
-				     struct erofs_map_blocks *map)
+static int z_erofs_lookup_pcluster(struct z_erofs_decompress_frontend *fe,
+				   struct inode *inode,
+				   struct erofs_map_blocks *map)
 {
 	struct z_erofs_pcluster *pcl = fe->pcl;
-	struct z_erofs_collection *cl;
 	unsigned int length;
 
 	/* to avoid unexpected loop formed by corrupted images */
@@ -419,8 +417,7 @@ static int z_erofs_lookup_collection(struct z_erofs_decompress_frontend *fe,
 		return -EFSCORRUPTED;
 	}
 
-	cl = z_erofs_primarycollection(pcl);
-	if (cl->pageofs != (map->m_la & ~PAGE_MASK)) {
+	if (pcl->pageofs_out != (map->m_la & ~PAGE_MASK)) {
 		DBG_BUGON(1);
 		return -EFSCORRUPTED;
 	}
@@ -443,23 +440,21 @@ static int z_erofs_lookup_collection(struct z_erofs_decompress_frontend *fe,
 			length = READ_ONCE(pcl->length);
 		}
 	}
-	mutex_lock(&cl->lock);
+	mutex_lock(&pcl->lock);
 	/* used to check tail merging loop due to corrupted images */
 	if (fe->owned_head == Z_EROFS_PCLUSTER_TAIL)
 		fe->tailpcl = pcl;
 
 	z_erofs_try_to_claim_pcluster(fe);
-	fe->cl = cl;
 	return 0;
 }
 
-static int z_erofs_register_collection(struct z_erofs_decompress_frontend *fe,
-				       struct inode *inode,
-				       struct erofs_map_blocks *map)
+static int z_erofs_register_pcluster(struct z_erofs_decompress_frontend *fe,
+				     struct inode *inode,
+				     struct erofs_map_blocks *map)
 {
 	bool ztailpacking = map->m_flags & EROFS_MAP_META;
 	struct z_erofs_pcluster *pcl;
-	struct z_erofs_collection *cl;
 	struct erofs_workgroup *grp;
 	int err;
 
@@ -482,17 +477,15 @@ static int z_erofs_register_collection(struct z_erofs_decompress_frontend *fe,
 
 	/* new pclusters should be claimed as type 1, primary and followed */
 	pcl->next = fe->owned_head;
+	pcl->pageofs_out = map->m_la & ~PAGE_MASK;
 	fe->mode = COLLECT_PRIMARY_FOLLOWED;
 
-	cl = z_erofs_primarycollection(pcl);
-	cl->pageofs = map->m_la & ~PAGE_MASK;
-
 	/*
 	 * lock all primary followed works before visible to others
 	 * and mutex_trylock *never* fails for a new pcluster.
 	 */
-	mutex_init(&cl->lock);
-	DBG_BUGON(!mutex_trylock(&cl->lock));
+	mutex_init(&pcl->lock);
+	DBG_BUGON(!mutex_trylock(&pcl->lock));
 
 	if (ztailpacking) {
 		pcl->obj.index = 0;	/* which indicates ztailpacking */
@@ -519,11 +512,10 @@ static int z_erofs_register_collection(struct z_erofs_decompress_frontend *fe,
 		fe->tailpcl = pcl;
 	fe->owned_head = &pcl->next;
 	fe->pcl = pcl;
-	fe->cl = cl;
 	return 0;
 
 err_out:
-	mutex_unlock(&cl->lock);
+	mutex_unlock(&pcl->lock);
 	z_erofs_free_pcluster(pcl);
 	return err;
 }
@@ -535,9 +527,9 @@ static int z_erofs_collector_begin(struct z_erofs_decompress_frontend *fe,
 	struct erofs_workgroup *grp;
 	int ret;
 
-	DBG_BUGON(fe->cl);
+	DBG_BUGON(fe->pcl);
 
-	/* must be Z_EROFS_PCLUSTER_TAIL or pointed to previous collection */
+	/* must be Z_EROFS_PCLUSTER_TAIL or pointed to previous pcluster */
 	DBG_BUGON(fe->owned_head == Z_EROFS_PCLUSTER_NIL);
 	DBG_BUGON(fe->owned_head == Z_EROFS_PCLUSTER_TAIL_CLOSED);
 
@@ -554,14 +546,14 @@ static int z_erofs_collector_begin(struct z_erofs_decompress_frontend *fe,
 		fe->pcl = container_of(grp, struct z_erofs_pcluster, obj);
 	} else {
 tailpacking:
-		ret = z_erofs_register_collection(fe, inode, map);
+		ret = z_erofs_register_pcluster(fe, inode, map);
 		if (!ret)
 			goto out;
 		if (ret != -EEXIST)
 			return ret;
 	}
 
-	ret = z_erofs_lookup_collection(fe, inode, map);
+	ret = z_erofs_lookup_pcluster(fe, inode, map);
 	if (ret) {
 		erofs_workgroup_put(&fe->pcl->obj);
 		return ret;
@@ -569,7 +561,7 @@ tailpacking:
 
 out:
 	z_erofs_pagevec_ctor_init(&fe->vector, Z_EROFS_NR_INLINE_PAGEVECS,
-				  fe->cl->pagevec, fe->cl->vcnt);
+				  fe->pcl->pagevec, fe->pcl->vcnt);
 	/* since file-backed online pages are traversed in reverse order */
 	fe->icpage_ptr = fe->pcl->compressed_pages +
 			z_erofs_pclusterpages(fe->pcl);
@@ -582,48 +574,36 @@ out:
  */
 static void z_erofs_rcu_callback(struct rcu_head *head)
 {
-	struct z_erofs_collection *const cl =
-		container_of(head, struct z_erofs_collection, rcu);
-
-	z_erofs_free_pcluster(container_of(cl, struct z_erofs_pcluster,
-					   primary_collection));
+	z_erofs_free_pcluster(container_of(head,
+			struct z_erofs_pcluster, rcu));
 }
 
 void erofs_workgroup_free_rcu(struct erofs_workgroup *grp)
 {
 	struct z_erofs_pcluster *const pcl =
 		container_of(grp, struct z_erofs_pcluster, obj);
-	struct z_erofs_collection *const cl = z_erofs_primarycollection(pcl);
-
-	call_rcu(&cl->rcu, z_erofs_rcu_callback);
-}
 
-static void z_erofs_collection_put(struct z_erofs_collection *cl)
-{
-	struct z_erofs_pcluster *const pcl =
-		container_of(cl, struct z_erofs_pcluster, primary_collection);
-
-	erofs_workgroup_put(&pcl->obj);
+	call_rcu(&pcl->rcu, z_erofs_rcu_callback);
 }
 
 static bool z_erofs_collector_end(struct z_erofs_decompress_frontend *fe)
 {
-	struct z_erofs_collection *cl = fe->cl;
+	struct z_erofs_pcluster *pcl = fe->pcl;
 
-	if (!cl)
+	if (!pcl)
 		return false;
 
 	z_erofs_pagevec_ctor_exit(&fe->vector, false);
-	mutex_unlock(&cl->lock);
+	mutex_unlock(&pcl->lock);
 
 	/*
 	 * if all pending pages are added, don't hold its reference
 	 * any longer if the pcluster isn't hosted by ourselves.
 	 */
 	if (fe->mode < COLLECT_PRIMARY_FOLLOWED_NOINPLACE)
-		z_erofs_collection_put(cl);
+		erofs_workgroup_put(&pcl->obj);
 
-	fe->cl = NULL;
+	fe->pcl = NULL;
 	return true;
 }
 
@@ -663,28 +643,23 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
 repeat:
 	cur = end - 1;
 
-	/* lucky, within the range of the current map_blocks */
-	if (offset + cur >= map->m_la &&
-	    offset + cur < map->m_la + map->m_llen) {
-		/* didn't get a valid collection previously (very rare) */
-		if (!fe->cl)
-			goto restart_now;
-		goto hitted;
-	}
-
-	/* go ahead the next map_blocks */
-	erofs_dbg("%s: [out-of-range] pos %llu", __func__, offset + cur);
-
-	if (z_erofs_collector_end(fe))
-		fe->backmost = false;
+	if (offset + cur < map->m_la ||
+	    offset + cur >= map->m_la + map->m_llen) {
+		erofs_dbg("out-of-range map @ pos %llu", offset + cur);
 
-	map->m_la = offset + cur;
-	map->m_llen = 0;
-	err = z_erofs_map_blocks_iter(inode, map, 0);
-	if (err)
-		goto err_out;
+		if (z_erofs_collector_end(fe))
+			fe->backmost = false;
+		map->m_la = offset + cur;
+		map->m_llen = 0;
+		err = z_erofs_map_blocks_iter(inode, map, 0);
+		if (err)
+			goto err_out;
+	} else {
+		if (fe->pcl)
+			goto hitted;
+		/* didn't get a valid pcluster previously (very rare) */
+	}
 
-restart_now:
 	if (!(map->m_flags & EROFS_MAP_MAPPED))
 		goto hitted;
 
@@ -766,7 +741,7 @@ retry:
 	/* bump up the number of spiltted parts of a page */
 	++spiltted;
 	/* also update nr_pages */
-	fe->cl->nr_pages = max_t(pgoff_t, fe->cl->nr_pages, index + 1);
+	fe->pcl->nr_pages = max_t(pgoff_t, fe->pcl->nr_pages, index + 1);
 next_part:
 	/* can be used for verification */
 	map->m_llen = offset + cur - map->m_la;
@@ -821,15 +796,13 @@ static int z_erofs_decompress_pcluster(struct super_block *sb,
 
 	enum z_erofs_page_type page_type;
 	bool overlapped, partial;
-	struct z_erofs_collection *cl;
 	int err;
 
 	might_sleep();
-	cl = z_erofs_primarycollection(pcl);
-	DBG_BUGON(!READ_ONCE(cl->nr_pages));
+	DBG_BUGON(!READ_ONCE(pcl->nr_pages));
 
-	mutex_lock(&cl->lock);
-	nr_pages = cl->nr_pages;
+	mutex_lock(&pcl->lock);
+	nr_pages = pcl->nr_pages;
 
 	if (nr_pages <= Z_EROFS_VMAP_ONSTACK_PAGES) {
 		pages = pages_onstack;
@@ -857,9 +830,9 @@ static int z_erofs_decompress_pcluster(struct super_block *sb,
 
 	err = 0;
 	z_erofs_pagevec_ctor_init(&ctor, Z_EROFS_NR_INLINE_PAGEVECS,
-				  cl->pagevec, 0);
+				  pcl->pagevec, 0);
 
-	for (i = 0; i < cl->vcnt; ++i) {
+	for (i = 0; i < pcl->vcnt; ++i) {
 		unsigned int pagenr;
 
 		page = z_erofs_pagevec_dequeue(&ctor, &page_type);
@@ -945,11 +918,11 @@ static int z_erofs_decompress_pcluster(struct super_block *sb,
 		goto out;
 
 	llen = pcl->length >> Z_EROFS_PCLUSTER_LENGTH_BIT;
-	if (nr_pages << PAGE_SHIFT >= cl->pageofs + llen) {
+	if (nr_pages << PAGE_SHIFT >= pcl->pageofs_out + llen) {
 		outputsize = llen;
 		partial = !(pcl->length & Z_EROFS_PCLUSTER_FULL_LENGTH);
 	} else {
-		outputsize = (nr_pages << PAGE_SHIFT) - cl->pageofs;
+		outputsize = (nr_pages << PAGE_SHIFT) - pcl->pageofs_out;
 		partial = true;
 	}
 
@@ -963,7 +936,7 @@ static int z_erofs_decompress_pcluster(struct super_block *sb,
 					.in = compressed_pages,
 					.out = pages,
 					.pageofs_in = pcl->pageofs_in,
-					.pageofs_out = cl->pageofs,
+					.pageofs_out = pcl->pageofs_out,
 					.inputsize = inputsize,
 					.outputsize = outputsize,
 					.alg = pcl->algorithmformat,
@@ -1012,16 +985,12 @@ out:
 	else if (pages != pages_onstack)
 		kvfree(pages);
 
-	cl->nr_pages = 0;
-	cl->vcnt = 0;
+	pcl->nr_pages = 0;
+	pcl->vcnt = 0;
 
-	/* all cl locks MUST be taken before the following line */
+	/* pcluster lock MUST be taken before the following line */
 	WRITE_ONCE(pcl->next, Z_EROFS_PCLUSTER_NIL);
-
-	/* all cl locks SHOULD be released right now */
-	mutex_unlock(&cl->lock);
-
-	z_erofs_collection_put(cl);
+	mutex_unlock(&pcl->lock);
 	return err;
 }
 
@@ -1043,6 +1012,7 @@ static void z_erofs_decompress_queue(const struct z_erofs_decompressqueue *io,
 		owned = READ_ONCE(pcl->next);
 
 		z_erofs_decompress_pcluster(io->sb, pcl, pagepool);
+		erofs_workgroup_put(&pcl->obj);
 	}
 }
 
@@ -1466,22 +1436,19 @@ static void z_erofs_pcluster_readmore(struct z_erofs_decompress_frontend *f,
 		struct page *page;
 
 		page = erofs_grab_cache_page_nowait(inode->i_mapping, index);
-		if (!page)
-			goto skip;
-
-		if (PageUptodate(page)) {
-			unlock_page(page);
+		if (page) {
+			if (PageUptodate(page)) {
+				unlock_page(page);
+			} else {
+				err = z_erofs_do_read_page(f, page, pagepool);
+				if (err)
+					erofs_err(inode->i_sb,
+						  "readmore error at page %lu @ nid %llu",
+						  index, EROFS_I(inode)->nid);
+			}
 			put_page(page);
-			goto skip;
 		}
 
-		err = z_erofs_do_read_page(f, page, pagepool);
-		if (err)
-			erofs_err(inode->i_sb,
-				  "readmore error at page %lu @ nid %llu",
-				  index, EROFS_I(inode)->nid);
-		put_page(page);
-skip:
 		if (cur < PAGE_SIZE)
 			break;
 		cur = (index << PAGE_SHIFT) - 1;
diff --git a/fs/erofs/zdata.h b/fs/erofs/zdata.h
index 800b11c53f57..58053bb5066f 100644
--- a/fs/erofs/zdata.h
+++ b/fs/erofs/zdata.h
@@ -12,21 +12,40 @@
 #define Z_EROFS_PCLUSTER_MAX_PAGES	(Z_EROFS_PCLUSTER_MAX_SIZE / PAGE_SIZE)
 #define Z_EROFS_NR_INLINE_PAGEVECS      3
 
+#define Z_EROFS_PCLUSTER_FULL_LENGTH    0x00000001
+#define Z_EROFS_PCLUSTER_LENGTH_BIT     1
+
+/*
+ * let's leave a type here in case of introducing
+ * another tagged pointer later.
+ */
+typedef void *z_erofs_next_pcluster_t;
+
 /*
  * Structure fields follow one of the following exclusion rules.
  *
  * I: Modifiable by initialization/destruction paths and read-only
  *    for everyone else;
  *
- * L: Field should be protected by pageset lock;
+ * L: Field should be protected by the pcluster lock;
  *
  * A: Field should be accessed / updated in atomic for parallelized code.
  */
-struct z_erofs_collection {
+struct z_erofs_pcluster {
+	struct erofs_workgroup obj;
 	struct mutex lock;
 
+	/* A: point to next chained pcluster or TAILs */
+	z_erofs_next_pcluster_t next;
+
+	/* A: lower limit of decompressed length and if full length or not */
+	unsigned int length;
+
 	/* I: page offset of start position of decompression */
-	unsigned short pageofs;
+	unsigned short pageofs_out;
+
+	/* I: page offset of inline compressed data */
+	unsigned short pageofs_in;
 
 	/* L: maximum relative page index in pagevec[] */
 	unsigned short nr_pages;
@@ -41,29 +60,6 @@ struct z_erofs_collection {
 		/* I: can be used to free the pcluster by RCU. */
 		struct rcu_head rcu;
 	};
-};
-
-#define Z_EROFS_PCLUSTER_FULL_LENGTH    0x00000001
-#define Z_EROFS_PCLUSTER_LENGTH_BIT     1
-
-/*
- * let's leave a type here in case of introducing
- * another tagged pointer later.
- */
-typedef void *z_erofs_next_pcluster_t;
-
-struct z_erofs_pcluster {
-	struct erofs_workgroup obj;
-	struct z_erofs_collection primary_collection;
-
-	/* A: point to next chained pcluster or TAILs */
-	z_erofs_next_pcluster_t next;
-
-	/* A: lower limit of decompressed length and if full length or not */
-	unsigned int length;
-
-	/* I: page offset of inline compressed data */
-	unsigned short pageofs_in;
 
 	union {
 		/* I: physical cluster size in pages */
@@ -80,8 +76,6 @@ struct z_erofs_pcluster {
 	struct page *compressed_pages[];
 };
 
-#define z_erofs_primarycollection(pcluster) (&(pcluster)->primary_collection)
-
 /* let's avoid the valid 32-bit kernel addresses */
 
 /* the chained workgroup has't submitted io (still open) */