erofs: support unencoded inodes for page cache share

Hongbo Li · hsiangkao · commit 34096ba919fd · 2026-01-23T20:02:09.000+08:00
This patch adds inode page cache sharing functionality for unencoded
files.

I conducted experiments in the container environment. Below is the
memory usage for reading all files in two different minor versions
of container images:

+-------------------+------------------+-------------+---------------+
|       Image       | Page Cache Share | Memory (MB) |    Memory     |
|                   |                  |             | Reduction (%) |
+-------------------+------------------+-------------+---------------+
|                   |        No        |     241     |       -       |
|       redis       +------------------+-------------+---------------+
|   7.2.4 &amp; 7.2.5   |        Yes       |     163     |      33%      |
+-------------------+------------------+-------------+---------------+
|                   |        No        |     872     |       -       |
|      postgres     +------------------+-------------+---------------+
|    16.1 &amp; 16.2    |        Yes       |     630     |      28%      |
+-------------------+------------------+-------------+---------------+
|                   |        No        |     2771    |       -       |
|     tensorflow    +------------------+-------------+---------------+
|  2.11.0 &amp; 2.11.1  |        Yes       |     2340    |      16%      |
+-------------------+------------------+-------------+---------------+
|                   |        No        |     926     |       -       |
|       mysql       +------------------+-------------+---------------+
|  8.0.11 &amp; 8.0.12  |        Yes       |     735     |      21%      |
+-------------------+------------------+-------------+---------------+
|                   |        No        |     390     |       -       |
|       nginx       +------------------+-------------+---------------+
|   7.2.4 &amp; 7.2.5   |        Yes       |     219     |      44%      |
+-------------------+------------------+-------------+---------------+
|       tomcat      |        No        |     924     |       -       |
| 10.1.25 &amp; 10.1.26 +------------------+-------------+---------------+
|                   |        Yes       |     474     |      49%      |
+-------------------+------------------+-------------+---------------+

Additionally, the table below shows the runtime memory usage of the
container:

+-------------------+------------------+-------------+---------------+
|       Image       | Page Cache Share | Memory (MB) |    Memory     |
|                   |                  |             | Reduction (%) |
+-------------------+------------------+-------------+---------------+
|                   |        No        |      35     |       -       |
|       redis       +------------------+-------------+---------------+
|   7.2.4 &amp; 7.2.5   |        Yes       |      28     |      20%      |
+-------------------+------------------+-------------+---------------+
|                   |        No        |     149     |       -       |
|      postgres     +------------------+-------------+---------------+
|    16.1 &amp; 16.2    |        Yes       |      95     |      37%      |
+-------------------+------------------+-------------+---------------+
|                   |        No        |     1028    |       -       |
|     tensorflow    +------------------+-------------+---------------+
|  2.11.0 &amp; 2.11.1  |        Yes       |     930     |      10%      |
+-------------------+------------------+-------------+---------------+
|                   |        No        |     155     |       -       |
|       mysql       +------------------+-------------+---------------+
|  8.0.11 &amp; 8.0.12  |        Yes       |     132     |      15%      |
+-------------------+------------------+-------------+---------------+
|                   |        No        |      25     |       -       |
|       nginx       +------------------+-------------+---------------+
|   7.2.4 &amp; 7.2.5   |        Yes       |      20     |      20%      |
+-------------------+------------------+-------------+---------------+
|       tomcat      |        No        |     186     |       -       |
| 10.1.25 &amp; 10.1.26 +------------------+-------------+---------------+
|                   |        Yes       |      98     |      48%      |
+-------------------+------------------+-------------+---------------+

Co-developed-by: Hongzhen Luo &lt;hongzhen@linux.alibaba.com&gt;
Signed-off-by: Hongzhen Luo &lt;hongzhen@linux.alibaba.com&gt;
Signed-off-by: Hongbo Li &lt;lihongbo22@huawei.com&gt;
Reviewed-by: Gao Xiang &lt;hsiangkao@linux.alibaba.com&gt;
Signed-off-by: Gao Xiang &lt;hsiangkao@linux.alibaba.com&gt;
diff --git a/fs/erofs/data.c b/fs/erofs/data.c
@@ -269,21 +269,23 @@ void erofs_onlinefolio_end(struct folio *folio, int err, bool dirty)
 struct erofs_iomap_iter_ctx {
 	struct page *page;
 	void *base;
+	struct inode *realinode;
 };
 
 static int erofs_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
 		unsigned int flags, struct iomap *iomap, struct iomap *srcmap)
 {
 	struct iomap_iter *iter = container_of(iomap, struct iomap_iter, iomap);
 	struct erofs_iomap_iter_ctx *ctx = iter->private;
-	struct super_block *sb = inode->i_sb;
+	struct inode *realinode = ctx ? ctx->realinode : inode;
+	struct super_block *sb = realinode->i_sb;
 	struct erofs_map_blocks map;
 	struct erofs_map_dev mdev;
 	int ret;
 
 	map.m_la = offset;
 	map.m_llen = length;
-	ret = erofs_map_blocks(inode, &map);
+	ret = erofs_map_blocks(realinode, &map);
 	if (ret < 0)
 		return ret;
 
@@ -296,7 +298,7 @@ static int erofs_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
 		return 0;
 	}
 
-	if (!(map.m_flags & EROFS_MAP_META) || !erofs_inode_in_metabox(inode)) {
+	if (!(map.m_flags & EROFS_MAP_META) || !erofs_inode_in_metabox(realinode)) {
 		mdev = (struct erofs_map_dev) {
 			.m_deviceid = map.m_deviceid,
 			.m_pa = map.m_pa,
@@ -322,7 +324,7 @@ static int erofs_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
 			void *ptr;
 
 			ptr = erofs_read_metabuf(&buf, sb, map.m_pa,
-						 erofs_inode_in_metabox(inode));
+						 erofs_inode_in_metabox(realinode));
 			if (IS_ERR(ptr))
 				return PTR_ERR(ptr);
 			iomap->inline_data = ptr;
@@ -383,10 +385,15 @@ static int erofs_read_folio(struct file *file, struct folio *folio)
 		.ops		= &iomap_bio_read_ops,
 		.cur_folio	= folio,
 	};
-	struct erofs_iomap_iter_ctx iter_ctx = {};
+	bool need_iput;
+	struct erofs_iomap_iter_ctx iter_ctx = {
+		.realinode = erofs_real_inode(folio_inode(folio), &need_iput),
+	};
 
-	trace_erofs_read_folio(folio_inode(folio), folio, true);
+	trace_erofs_read_folio(iter_ctx.realinode, folio, true);
 	iomap_read_folio(&erofs_iomap_ops, &read_ctx, &iter_ctx);
+	if (need_iput)
+		iput(iter_ctx.realinode);
 	return 0;
 }
 
@@ -396,11 +403,16 @@ static void erofs_readahead(struct readahead_control *rac)
 		.ops		= &iomap_bio_read_ops,
 		.rac		= rac,
 	};
-	struct erofs_iomap_iter_ctx iter_ctx = {};
+	bool need_iput;
+	struct erofs_iomap_iter_ctx iter_ctx = {
+		.realinode = erofs_real_inode(rac->mapping->host, &need_iput),
+	};
 
-	trace_erofs_readahead(rac->mapping->host, readahead_index(rac),
+	trace_erofs_readahead(iter_ctx.realinode, readahead_index(rac),
 			      readahead_count(rac), true);
 	iomap_readahead(&erofs_iomap_ops, &read_ctx, &iter_ctx);
+	if (need_iput)
+		iput(iter_ctx.realinode);
 }
 
 static sector_t erofs_bmap(struct address_space *mapping, sector_t block)
@@ -421,7 +433,9 @@ static ssize_t erofs_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
 		return dax_iomap_rw(iocb, to, &erofs_iomap_ops);
 #endif
 	if ((iocb->ki_flags & IOCB_DIRECT) && inode->i_sb->s_bdev) {
-		struct erofs_iomap_iter_ctx iter_ctx = {};
+		struct erofs_iomap_iter_ctx iter_ctx = {
+			.realinode = inode,
+		};
 
 		return iomap_dio_rw(iocb, to, &erofs_iomap_ops,
 				    NULL, 0, &iter_ctx, 0);
diff --git a/fs/erofs/fileio.c b/fs/erofs/fileio.c
@@ -88,9 +88,9 @@ void erofs_fileio_submit_bio(struct bio *bio)
 						   bio));
 }
 
-static int erofs_fileio_scan_folio(struct erofs_fileio *io, struct folio *folio)
+static int erofs_fileio_scan_folio(struct erofs_fileio *io,
+				   struct inode *inode, struct folio *folio)
 {
-	struct inode *inode = folio_inode(folio);
 	struct erofs_map_blocks *map = &io->map;
 	unsigned int cur = 0, end = folio_size(folio), len, attached = 0;
 	loff_t pos = folio_pos(folio), ofs;
@@ -158,31 +158,38 @@ static int erofs_fileio_scan_folio(struct erofs_fileio *io, struct folio *folio)
 
 static int erofs_fileio_read_folio(struct file *file, struct folio *folio)
 {
+	bool need_iput;
+	struct inode *realinode = erofs_real_inode(folio_inode(folio), &need_iput);
 	struct erofs_fileio io = {};
 	int err;
 
-	trace_erofs_read_folio(folio_inode(folio), folio, true);
-	err = erofs_fileio_scan_folio(&io, folio);
+	trace_erofs_read_folio(realinode, folio, true);
+	err = erofs_fileio_scan_folio(&io, realinode, folio);
 	erofs_fileio_rq_submit(io.rq);
+	if (need_iput)
+		iput(realinode);
 	return err;
 }
 
 static void erofs_fileio_readahead(struct readahead_control *rac)
 {
-	struct inode *inode = rac->mapping->host;
+	bool need_iput;
+	struct inode *realinode = erofs_real_inode(rac->mapping->host, &need_iput);
 	struct erofs_fileio io = {};
 	struct folio *folio;
 	int err;
 
-	trace_erofs_readahead(inode, readahead_index(rac),
+	trace_erofs_readahead(realinode, readahead_index(rac),
 			      readahead_count(rac), true);
 	while ((folio = readahead_folio(rac))) {
-		err = erofs_fileio_scan_folio(&io, folio);
+		err = erofs_fileio_scan_folio(&io, realinode, folio);
 		if (err && err != -EINTR)
-			erofs_err(inode->i_sb, "readahead error at folio %lu @ nid %llu",
-				  folio->index, EROFS_I(inode)->nid);
+			erofs_err(realinode->i_sb, "readahead error at folio %lu @ nid %llu",
+				  folio->index, EROFS_I(realinode)->nid);
 	}
 	erofs_fileio_rq_submit(io.rq);
+	if (need_iput)
+		iput(realinode);
 }
 
 const struct address_space_operations erofs_fileio_aops = {
diff --git a/fs/erofs/inode.c b/fs/erofs/inode.c
@@ -213,7 +213,8 @@ static int erofs_fill_inode(struct inode *inode)
 	switch (inode->i_mode & S_IFMT) {
 	case S_IFREG:
 		inode->i_op = &erofs_generic_iops;
-		inode->i_fop = &erofs_file_fops;
+		inode->i_fop = erofs_ishare_fill_inode(inode) ?
+			       &erofs_ishare_fops : &erofs_file_fops;
 		break;
 	case S_IFDIR:
 		inode->i_op = &erofs_dir_iops;
diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
@@ -584,11 +584,17 @@ int __init erofs_init_ishare(void);
 void erofs_exit_ishare(void);
 bool erofs_ishare_fill_inode(struct inode *inode);
 void erofs_ishare_free_inode(struct inode *inode);
+struct inode *erofs_real_inode(struct inode *inode, bool *need_iput);
 #else
 static inline int erofs_init_ishare(void) { return 0; }
 static inline void erofs_exit_ishare(void) {}
 static inline bool erofs_ishare_fill_inode(struct inode *inode) { return false; }
 static inline void erofs_ishare_free_inode(struct inode *inode) {}
+static inline struct inode *erofs_real_inode(struct inode *inode, bool *need_iput)
+{
+	*need_iput = false;
+	return inode;
+}
 #endif
 
 long erofs_ioctl(struct file *filp, unsigned int cmd, unsigned long arg);
diff --git a/fs/erofs/ishare.c b/fs/erofs/ishare.c
@@ -11,6 +11,12 @@
 
 static struct vfsmount *erofs_ishare_mnt;
 
+static inline bool erofs_is_ishare_inode(struct inode *inode)
+{
+	/* assumed FS_ONDEMAND is excluded with FS_PAGE_CACHE_SHARE feature */
+	return inode->i_sb->s_type == &erofs_anon_fs_type;
+}
+
 static int erofs_ishare_iget5_eq(struct inode *inode, void *data)
 {
 	struct erofs_inode_fingerprint *fp1 = &EROFS_I(inode)->fingerprint;
@@ -38,6 +44,8 @@ bool erofs_ishare_fill_inode(struct inode *inode)
 	struct inode *sharedinode;
 	unsigned long hash;
 
+	if (erofs_inode_is_data_compressed(vi->datalayout))
+		return false;
 	if (erofs_xattr_fill_inode_fingerprint(&fp, inode, sbi->domain_id))
 		return false;
 	hash = xxh32(fp.opaque, fp.size, 0);
@@ -155,6 +163,32 @@ const struct file_operations erofs_ishare_fops = {
 	.splice_read	= filemap_splice_read,
 };
 
+struct inode *erofs_real_inode(struct inode *inode, bool *need_iput)
+{
+	struct erofs_inode *vi, *vi_share;
+	struct inode *realinode;
+
+	*need_iput = false;
+	if (!erofs_is_ishare_inode(inode))
+		return inode;
+
+	vi_share = EROFS_I(inode);
+	spin_lock(&vi_share->ishare_lock);
+	/* fetch any one as real inode */
+	DBG_BUGON(list_empty(&vi_share->ishare_list));
+	list_for_each_entry(vi, &vi_share->ishare_list, ishare_list) {
+		realinode = igrab(&vi->vfs_inode);
+		if (realinode) {
+			*need_iput = true;
+			break;
+		}
+	}
+	spin_unlock(&vi_share->ishare_lock);
+
+	DBG_BUGON(!realinode);
+	return realinode;
+}
+
 int __init erofs_init_ishare(void)
 {
 	erofs_ishare_mnt = kern_mount(&erofs_anon_fs_type);
