erofs: use meta buffers for zmap operations

Get rid of old erofs_get_meta_page() within zmap operations by
using on-stack meta buffers in order to prepare subpage and folio
features.

Finally, erofs_get_meta_page() is useless. Get rid of it!

Link: https://lore.kernel.org/r/20220102040017.51352-6-hsiangkao@linux.alibaba.comReviewed-by: Yue Hu <huyue2@yulong.com>
Reviewed-by: Liu Bo <bo.liu@linux.alibaba.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

fs/erofs/data.c

@@ -9,19 +9,6 @@
 #include <linux/dax.h>
 #include <trace/events/erofs.h>
 
-struct page *erofs_get_meta_page(struct super_block *sb, erofs_blk_t blkaddr)
-{
-	struct address_space *const mapping = sb->s_bdev->bd_inode->i_mapping;
-	struct page *page;
-
-	page = read_cache_page_gfp(mapping, blkaddr,
-				   mapping_gfp_constraint(mapping, ~__GFP_FS));
-	/* should already be PageUptodate */
-	if (!IS_ERR(page))
-		lock_page(page);
-	return page;
-}
-
 void erofs_unmap_metabuf(struct erofs_buf *buf)
 {
 	if (buf->kmap_type == EROFS_KMAP)

fs/erofs/internal.h

@@ -419,14 +419,14 @@ enum {
 #define EROFS_MAP_FULL_MAPPED	(1 << BH_FullMapped)
 
 struct erofs_map_blocks {
+	struct erofs_buf buf;
+
 	erofs_off_t m_pa, m_la;
 	u64 m_plen, m_llen;
 
 	unsigned short m_deviceid;
 	char m_algorithmformat;
 	unsigned int m_flags;
-
-	struct page *mpage;
 };
 
 /* Flags used by erofs_map_blocks_flatmode() */
@@ -474,7 +474,7 @@ struct erofs_map_dev {
 
 /* data.c */
 extern const struct file_operations erofs_file_fops;
-struct page *erofs_get_meta_page(struct super_block *sb, erofs_blk_t blkaddr);
+void erofs_unmap_metabuf(struct erofs_buf *buf);
 void erofs_put_metabuf(struct erofs_buf *buf);
 void *erofs_read_metabuf(struct erofs_buf *buf, struct super_block *sb,
 			 erofs_blk_t blkaddr, enum erofs_kmap_type type);

fs/erofs/zdata.c

@@ -698,20 +698,18 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
 		goto err_out;
 
 	if (z_erofs_is_inline_pcluster(clt->pcl)) {
-		struct page *mpage;
+		void *mp;
 
-		mpage = erofs_get_meta_page(inode->i_sb,
-					    erofs_blknr(map->m_pa));
-		if (IS_ERR(mpage)) {
-			err = PTR_ERR(mpage);
+		mp = erofs_read_metabuf(&fe->map.buf, inode->i_sb,
+					erofs_blknr(map->m_pa), EROFS_NO_KMAP);
+		if (IS_ERR(mp)) {
+			err = PTR_ERR(mp);
 			erofs_err(inode->i_sb,
 				  "failed to get inline page, err %d", err);
 			goto err_out;
 		}
-		/* TODO: new subpage feature will get rid of it */
-		unlock_page(mpage);
-
-		WRITE_ONCE(clt->pcl->compressed_pages[0], mpage);
+		get_page(fe->map.buf.page);
+		WRITE_ONCE(clt->pcl->compressed_pages[0], fe->map.buf.page);
 		clt->mode = COLLECT_PRIMARY_FOLLOWED_NOINPLACE;
 	} else {
 		/* preload all compressed pages (can change mode if needed) */
@@ -1529,9 +1527,7 @@ static int z_erofs_readpage(struct file *file, struct page *page)
 	if (err)
 		erofs_err(inode->i_sb, "failed to read, err [%d]", err);
 
-	if (f.map.mpage)
-		put_page(f.map.mpage);
-
+	erofs_put_metabuf(&f.map.buf);
 	erofs_release_pages(&pagepool);
 	return err;
 }
@@ -1576,8 +1572,7 @@ static void z_erofs_readahead(struct readahead_control *rac)
 
 	z_erofs_runqueue(inode->i_sb, &f, &pagepool,
 			 z_erofs_get_sync_decompress_policy(sbi, nr_pages));
-	if (f.map.mpage)
-		put_page(f.map.mpage);
+	erofs_put_metabuf(&f.map.buf);
 	erofs_release_pages(&pagepool);
 }
 

fs/erofs/zmap.c

@@ -35,7 +35,7 @@ static int z_erofs_fill_inode_lazy(struct inode *inode)
 	struct super_block *const sb = inode->i_sb;
 	int err, headnr;
 	erofs_off_t pos;
-	struct page *page;
+	struct erofs_buf buf = __EROFS_BUF_INITIALIZER;
 	void *kaddr;
 	struct z_erofs_map_header *h;
 
@@ -61,14 +61,13 @@ static int z_erofs_fill_inode_lazy(struct inode *inode)
 
 	pos = ALIGN(iloc(EROFS_SB(sb), vi->nid) + vi->inode_isize +
 		    vi->xattr_isize, 8);
-	page = erofs_get_meta_page(sb, erofs_blknr(pos));
-	if (IS_ERR(page)) {
-		err = PTR_ERR(page);
+	kaddr = erofs_read_metabuf(&buf, sb, erofs_blknr(pos),
+				   EROFS_KMAP_ATOMIC);
+	if (IS_ERR(kaddr)) {
+		err = PTR_ERR(kaddr);
 		goto out_unlock;
 	}
 
-	kaddr = kmap_atomic(page);
-
 	h = kaddr + erofs_blkoff(pos);
 	vi->z_advise = le16_to_cpu(h->h_advise);
 	vi->z_algorithmtype[0] = h->h_algorithmtype & 15;
@@ -101,20 +100,19 @@ static int z_erofs_fill_inode_lazy(struct inode *inode)
 		goto unmap_done;
 	}
 unmap_done:
-	kunmap_atomic(kaddr);
-	unlock_page(page);
-	put_page(page);
+	erofs_put_metabuf(&buf);
 	if (err)
 		goto out_unlock;
 
 	if (vi->z_advise & Z_EROFS_ADVISE_INLINE_PCLUSTER) {
-		struct erofs_map_blocks map = { .mpage = NULL };
+		struct erofs_map_blocks map = {
+			.buf = __EROFS_BUF_INITIALIZER
+		};
 
 		vi->z_idata_size = le16_to_cpu(h->h_idata_size);
 		err = z_erofs_do_map_blocks(inode, &map,
 					    EROFS_GET_BLOCKS_FINDTAIL);
-		if (map.mpage)
-			put_page(map.mpage);
+		erofs_put_metabuf(&map.buf);
 
 		if (!map.m_plen ||
 		    erofs_blkoff(map.m_pa) + map.m_plen > EROFS_BLKSIZ) {
@@ -151,31 +149,11 @@ static int z_erofs_reload_indexes(struct z_erofs_maprecorder *m,
 				  erofs_blk_t eblk)
 {
 	struct super_block *const sb = m->inode->i_sb;
-	struct erofs_map_blocks *const map = m->map;
-	struct page *mpage = map->mpage;
-
-	if (mpage) {
-		if (mpage->index == eblk) {
-			if (!m->kaddr)
-				m->kaddr = kmap_atomic(mpage);
-			return 0;
-		}
 
-		if (m->kaddr) {
-			kunmap_atomic(m->kaddr);
-			m->kaddr = NULL;
-		}
-		put_page(mpage);
-	}
-
-	mpage = erofs_get_meta_page(sb, eblk);
-	if (IS_ERR(mpage)) {
-		map->mpage = NULL;
-		return PTR_ERR(mpage);
-	}
-	m->kaddr = kmap_atomic(mpage);
-	unlock_page(mpage);
-	map->mpage = mpage;
+	m->kaddr = erofs_read_metabuf(&m->map->buf, sb, eblk,
+				      EROFS_KMAP_ATOMIC);
+	if (IS_ERR(m->kaddr))
+		return PTR_ERR(m->kaddr);
 	return 0;
 }
 
@@ -711,8 +689,7 @@ static int z_erofs_do_map_blocks(struct inode *inode,
 			map->m_flags |= EROFS_MAP_FULL_MAPPED;
 	}
 unmap_out:
-	if (m.kaddr)
-		kunmap_atomic(m.kaddr);
+	erofs_unmap_metabuf(&m.map->buf);
 
 out:
 	erofs_dbg("%s, m_la %llu m_pa %llu m_llen %llu m_plen %llu m_flags 0%o",
@@ -759,8 +736,7 @@ static int z_erofs_iomap_begin_report(struct inode *inode, loff_t offset,
 	struct erofs_map_blocks map = { .m_la = offset };
 
 	ret = z_erofs_map_blocks_iter(inode, &map, EROFS_GET_BLOCKS_FIEMAP);
-	if (map.mpage)
-		put_page(map.mpage);
+	erofs_put_metabuf(&map.buf);
 	if (ret < 0)
 		return ret;