erofs: avoid obsolete {collector,collection} terms

{collector,collection} were once reserved in order to indicate different
runtime logical extent instance of multi-reference pclusters.

However, de-duplicated decompression has been landed in a more flexable
way, thus `struct z_erofs_collection` was formally removed in commit
87ca34a7 ("erofs: get rid of `struct z_erofs_collection'").

Let's handle the remaining leftovers, for example:
    `z_erofs_collector_begin` => `z_erofs_pcluster_begin`
    `z_erofs_collector_end` => `z_erofs_pcluster_end`

as well as some comments.  No logic changes.
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/20230817082813.81180-2-hsiangkao@linux.alibaba.com

fs/erofs/zdata.c

@@ -507,19 +507,17 @@ enum z_erofs_pclustermode {
 	 */
 	Z_EROFS_PCLUSTER_FOLLOWED_NOINPLACE,
 	/*
-	 * The current collection has been linked with the owned chain, and
-	 * could also be linked with the remaining collections, which means
-	 * if the processing page is the tail page of the collection, thus
-	 * the current collection can safely use the whole page (since
-	 * the previous collection is under control) for in-place I/O, as
-	 * illustrated below:
-	 *  ________________________________________________________________
-	 * |  tail (partial) page |          head (partial) page           |
-	 * |  (of the current cl) |      (of the previous collection)      |
-	 * |                      |                                        |
-	 * |__PCLUSTER_FOLLOWED___|___________PCLUSTER_FOLLOWED____________|
+	 * The pcluster was just linked to a decompression chain by us.  It can
+	 * also be linked with the remaining pclusters, which means if the
+	 * processing page is the tail page of a pcluster, this pcluster can
+	 * safely use the whole page (since the previous pcluster is within the
+	 * same chain) for in-place I/O, as illustrated below:
+	 *  ___________________________________________________
+	 * |  tail (partial) page  |    head (partial) page    |
+	 * |  (of the current pcl) |   (of the previous pcl)   |
+	 * |___PCLUSTER_FOLLOWED___|_____PCLUSTER_FOLLOWED_____|
 	 *
-	 * [  (*) the above page can be used as inplace I/O.               ]
+	 * [  (*) the page above can be used as inplace I/O.   ]
 	 */
 	Z_EROFS_PCLUSTER_FOLLOWED,
 };
@@ -851,7 +849,7 @@ static int z_erofs_register_pcluster(struct z_erofs_decompress_frontend *fe)
 	return err;
 }
 
-static int z_erofs_collector_begin(struct z_erofs_decompress_frontend *fe)
+static int z_erofs_pcluster_begin(struct z_erofs_decompress_frontend *fe)
 {
 	struct erofs_map_blocks *map = &fe->map;
 	struct erofs_workgroup *grp = NULL;
@@ -908,12 +906,12 @@ void erofs_workgroup_free_rcu(struct erofs_workgroup *grp)
 	call_rcu(&pcl->rcu, z_erofs_rcu_callback);
 }
 
-static bool z_erofs_collector_end(struct z_erofs_decompress_frontend *fe)
+static void z_erofs_pcluster_end(struct z_erofs_decompress_frontend *fe)
 {
 	struct z_erofs_pcluster *pcl = fe->pcl;
 
 	if (!pcl)
-		return false;
+		return;
 
 	z_erofs_bvec_iter_end(&fe->biter);
 	mutex_unlock(&pcl->lock);
@@ -929,7 +927,7 @@ static bool z_erofs_collector_end(struct z_erofs_decompress_frontend *fe)
 		erofs_workgroup_put(&pcl->obj);
 
 	fe->pcl = NULL;
-	return true;
+	fe->backmost = false;
 }
 
 static int z_erofs_read_fragment(struct super_block *sb, struct page *page,
@@ -978,8 +976,7 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
 
 	if (offset + cur < map->m_la ||
 	    offset + cur >= map->m_la + map->m_llen) {
-		if (z_erofs_collector_end(fe))
-			fe->backmost = false;
+		z_erofs_pcluster_end(fe);
 		map->m_la = offset + cur;
 		map->m_llen = 0;
 		err = z_erofs_map_blocks_iter(inode, map, 0);
@@ -995,7 +992,7 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
 	    map->m_flags & EROFS_MAP_FRAGMENT)
 		goto hitted;
 
-	err = z_erofs_collector_begin(fe);
+	err = z_erofs_pcluster_begin(fe);
 	if (err)
 		goto out;
 
@@ -1862,7 +1859,7 @@ static int z_erofs_read_folio(struct file *file, struct folio *folio)
 	z_erofs_pcluster_readmore(&f, NULL, true);
 	err = z_erofs_do_read_page(&f, page);
 	z_erofs_pcluster_readmore(&f, NULL, false);
-	(void)z_erofs_collector_end(&f);
+	z_erofs_pcluster_end(&f);
 
 	/* if some compressed cluster ready, need submit them anyway */
 	z_erofs_runqueue(&f, z_erofs_is_sync_decompress(sbi, 0), false);
@@ -1909,7 +1906,7 @@ static void z_erofs_readahead(struct readahead_control *rac)
 		put_page(page);
 	}
 	z_erofs_pcluster_readmore(&f, rac, false);
-	(void)z_erofs_collector_end(&f);
+	z_erofs_pcluster_end(&f);
 
 	z_erofs_runqueue(&f, z_erofs_is_sync_decompress(sbi, nr_pages), true);
 	erofs_put_metabuf(&f.map.buf);