[PATCH v5] ovl: whiteout inode sharing

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Sharing inode with different whiteout files for saving
inode and speeding up deleting operation.

Signed-off-by: Chengguang Xu <cgxu519@xxxxxxxxxxxx>
Reviewed-by: Amir Goldstein <amir73il@xxxxxxxxx>
---
v1->v2:
- Address Amir's comments in v1.

v2->v3:
- Address Amir's comments in v2.
- Rebase on Amir's "Overlayfs use index dir as work dir" patch set.
- Keep at most one whiteout tmpfile in work dir.

v3->v4:
- Disable the feature after link failure.
- Add mount option(whiteout link max) for overlayfs instance. 

v4->v5:
- Add a warning when mount option exceeds module parameter.

 fs/overlayfs/dir.c       | 47 ++++++++++++++++++++++++++++++++++------
 fs/overlayfs/overlayfs.h | 10 +++++++--
 fs/overlayfs/ovl_entry.h |  5 +++++
 fs/overlayfs/readdir.c   |  3 ++-
 fs/overlayfs/super.c     | 27 +++++++++++++++++++++++
 fs/overlayfs/util.c      |  3 ++-
 6 files changed, 84 insertions(+), 11 deletions(-)

diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
index 279009dee366..8b7d8854f31f 100644
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -62,35 +62,67 @@ struct dentry *ovl_lookup_temp(struct dentry *workdir)
 }
 
 /* caller holds i_mutex on workdir */
-static struct dentry *ovl_whiteout(struct dentry *workdir)
+static struct dentry *ovl_whiteout(struct ovl_fs *ofs, struct dentry *workdir)
 {
 	int err;
+	bool retried = false;
+	bool should_link = (ofs->whiteout_link_max > 1);
 	struct dentry *whiteout;
 	struct inode *wdir = workdir->d_inode;
 
+retry:
 	whiteout = ovl_lookup_temp(workdir);
 	if (IS_ERR(whiteout))
 		return whiteout;
 
+	err = 0;
+	if (should_link) {
+		if (ovl_whiteout_linkable(ofs)) {
+			err = ovl_do_link(ofs->whiteout, wdir, whiteout);
+			if (!err)
+				return whiteout;
+		} else if (ofs->whiteout) {
+			dput(whiteout);
+			whiteout = ofs->whiteout;
+			ofs->whiteout = NULL;
+			return whiteout;
+		}
+
+		if (err) {
+			pr_warn("Failed to link whiteout - disabling whiteout inode sharing(nlink=%u, err=%i)\n",
+				ofs->whiteout->d_inode->i_nlink, err);
+			ofs->whiteout_link_max = 0;
+			should_link = false;
+			ovl_cleanup(wdir, ofs->whiteout);
+			dput(ofs->whiteout);
+			ofs->whiteout = NULL;
+		}
+	}
+
 	err = ovl_do_whiteout(wdir, whiteout);
 	if (err) {
 		dput(whiteout);
-		whiteout = ERR_PTR(err);
+		return ERR_PTR(err);
 	}
 
-	return whiteout;
+	if (!should_link || retried)
+		return whiteout;
+
+	ofs->whiteout = whiteout;
+	retried = true;
+	goto retry;
 }
 
 /* Caller must hold i_mutex on both workdir and dir */
-int ovl_cleanup_and_whiteout(struct dentry *workdir, struct inode *dir,
-			     struct dentry *dentry)
+int ovl_cleanup_and_whiteout(struct ovl_fs *ofs, struct dentry *workdir,
+			     struct inode *dir, struct dentry *dentry)
 {
 	struct inode *wdir = workdir->d_inode;
 	struct dentry *whiteout;
 	int err;
 	int flags = 0;
 
-	whiteout = ovl_whiteout(workdir);
+	whiteout = ovl_whiteout(ofs, workdir);
 	err = PTR_ERR(whiteout);
 	if (IS_ERR(whiteout))
 		return err;
@@ -715,6 +747,7 @@ static bool ovl_matches_upper(struct dentry *dentry, struct dentry *upper)
 static int ovl_remove_and_whiteout(struct dentry *dentry,
 				   struct list_head *list)
 {
+	struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
 	struct dentry *workdir = ovl_workdir(dentry);
 	struct dentry *upperdir = ovl_dentry_upper(dentry->d_parent);
 	struct dentry *upper;
@@ -748,7 +781,7 @@ static int ovl_remove_and_whiteout(struct dentry *dentry,
 		goto out_dput_upper;
 	}
 
-	err = ovl_cleanup_and_whiteout(workdir, d_inode(upperdir), upper);
+	err = ovl_cleanup_and_whiteout(ofs, workdir, d_inode(upperdir), upper);
 	if (err)
 		goto out_d_drop;
 
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index e00b1ff6dea9..3b127c997a6d 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -225,6 +225,12 @@ static inline bool ovl_open_flags_need_copy_up(int flags)
 	return ((OPEN_FMODE(flags) & FMODE_WRITE) || (flags & O_TRUNC));
 }
 
+static inline bool ovl_whiteout_linkable(struct ovl_fs *ofs)
+{
+	return (ofs->whiteout &&
+		ofs->whiteout->d_inode->i_nlink < ofs->whiteout_link_max);
+}
+
 /* util.c */
 int ovl_want_write(struct dentry *dentry);
 void ovl_drop_write(struct dentry *dentry);
@@ -455,8 +461,8 @@ static inline void ovl_copyflags(struct inode *from, struct inode *to)
 
 /* dir.c */
 extern const struct inode_operations ovl_dir_inode_operations;
-int ovl_cleanup_and_whiteout(struct dentry *workdir, struct inode *dir,
-			     struct dentry *dentry);
+int ovl_cleanup_and_whiteout(struct ovl_fs *ofs, struct dentry *workdir,
+			     struct inode *dir, struct dentry *dentry);
 struct ovl_cattr {
 	dev_t rdev;
 	umode_t mode;
diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
index 5762d802fe01..c805c35e0594 100644
--- a/fs/overlayfs/ovl_entry.h
+++ b/fs/overlayfs/ovl_entry.h
@@ -17,6 +17,7 @@ struct ovl_config {
 	bool nfs_export;
 	int xino;
 	bool metacopy;
+	unsigned int whiteout_link_max;
 };
 
 struct ovl_sb {
@@ -77,6 +78,10 @@ struct ovl_fs {
 	int xino_mode;
 	/* For allocation of non-persistent inode numbers */
 	atomic_long_t last_ino;
+	/* Whiteout dentry cache */
+	struct dentry *whiteout;
+	/* Whiteout max link count */
+	unsigned int whiteout_link_max;
 };
 
 static inline struct ovl_fs *OVL_FS(struct super_block *sb)
diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c
index 20f5310d3ee4..bf22fb7792c1 100644
--- a/fs/overlayfs/readdir.c
+++ b/fs/overlayfs/readdir.c
@@ -1154,7 +1154,8 @@ int ovl_indexdir_cleanup(struct ovl_fs *ofs)
 			 * Whiteout orphan index to block future open by
 			 * handle after overlay nlink dropped to zero.
 			 */
-			err = ovl_cleanup_and_whiteout(indexdir, dir, index);
+			err = ovl_cleanup_and_whiteout(ofs, indexdir, dir,
+						       index);
 		} else {
 			/* Cleanup orphan index entries */
 			err = ovl_cleanup(dir, index);
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index f57aa348dcd6..af837e2910aa 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -26,6 +26,10 @@ struct ovl_dir_cache;
 
 #define OVL_MAX_STACK 500
 
+static unsigned int ovl_whiteout_link_max_def = 60000;
+module_param_named(whiteout_link_max, ovl_whiteout_link_max_def, uint, 0644);
+MODULE_PARM_DESC(whiteout_link_max, "Maximum count of whiteout file link");
+
 static bool ovl_redirect_dir_def = IS_ENABLED(CONFIG_OVERLAY_FS_REDIRECT_DIR);
 module_param_named(redirect_dir, ovl_redirect_dir_def, bool, 0644);
 MODULE_PARM_DESC(redirect_dir,
@@ -219,6 +223,7 @@ static void ovl_free_fs(struct ovl_fs *ofs)
 	iput(ofs->upperdir_trap);
 	dput(ofs->indexdir);
 	dput(ofs->workdir);
+	dput(ofs->whiteout);
 	if (ofs->workdir_locked)
 		ovl_inuse_unlock(ofs->workbasedir);
 	dput(ofs->workbasedir);
@@ -358,6 +363,10 @@ static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
 	if (ofs->config.metacopy != ovl_metacopy_def)
 		seq_printf(m, ",metacopy=%s",
 			   ofs->config.metacopy ? "on" : "off");
+	if (ofs->config.whiteout_link_max != ovl_whiteout_link_max_def)
+		seq_printf(m, ",whiteout_link_max=%u",
+			   ofs->config.whiteout_link_max);
+
 	return 0;
 }
 
@@ -398,6 +407,7 @@ enum {
 	OPT_XINO_AUTO,
 	OPT_METACOPY_ON,
 	OPT_METACOPY_OFF,
+	OPT_WHITEOUT_LINK_MAX,
 	OPT_ERR,
 };
 
@@ -416,6 +426,7 @@ static const match_table_t ovl_tokens = {
 	{OPT_XINO_AUTO,			"xino=auto"},
 	{OPT_METACOPY_ON,		"metacopy=on"},
 	{OPT_METACOPY_OFF,		"metacopy=off"},
+	{OPT_WHITEOUT_LINK_MAX,		"whiteout_link_max=%u"},
 	{OPT_ERR,			NULL}
 };
 
@@ -469,6 +480,7 @@ static int ovl_parse_opt(char *opt, struct ovl_config *config)
 {
 	char *p;
 	int err;
+	int link_max;
 	bool metacopy_opt = false, redirect_opt = false;
 	bool nfs_export_opt = false, index_opt = false;
 
@@ -560,6 +572,16 @@ static int ovl_parse_opt(char *opt, struct ovl_config *config)
 			metacopy_opt = true;
 			break;
 
+		case OPT_WHITEOUT_LINK_MAX:
+			if (match_int(&args[0], &link_max))
+				return -EINVAL;
+			if (link_max < ovl_whiteout_link_max_def) {
+				config->whiteout_link_max = link_max;
+				pr_warn("mount option whiteout_link_max=%u exceeds module parameter, set it equal to module parameter %u",
+					link_max, ovl_whiteout_link_max_def);
+			}
+			break;
+
 		default:
 			pr_err("unrecognized mount option \"%s\" or missing value\n",
 					p);
@@ -1269,6 +1291,10 @@ static int ovl_make_workdir(struct super_block *sb, struct ovl_fs *ofs,
 		pr_warn("NFS export requires \"index=on\", falling back to nfs_export=off.\n");
 		ofs->config.nfs_export = false;
 	}
+
+	ofs->whiteout_link_max = min_not_zero(
+		ofs->workdir->d_sb->s_max_links,
+		ofs->config.whiteout_link_max ?: 1);
 out:
 	mnt_drop_write(mnt);
 	return err;
@@ -1768,6 +1794,7 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 	ofs->config.nfs_export = ovl_nfs_export_def;
 	ofs->config.xino = ovl_xino_def();
 	ofs->config.metacopy = ovl_metacopy_def;
+	ofs->config.whiteout_link_max = ovl_whiteout_link_max_def;
 	err = ovl_parse_opt((char *) data, &ofs->config);
 	if (err)
 		goto out_err;
diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
index 36b60788ee47..18df65ee81a8 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -669,6 +669,7 @@ bool ovl_need_index(struct dentry *dentry)
 /* Caller must hold OVL_I(inode)->lock */
 static void ovl_cleanup_index(struct dentry *dentry)
 {
+	struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
 	struct dentry *indexdir = ovl_indexdir(dentry->d_sb);
 	struct inode *dir = indexdir->d_inode;
 	struct dentry *lowerdentry = ovl_dentry_lower(dentry);
@@ -707,7 +708,7 @@ static void ovl_cleanup_index(struct dentry *dentry)
 		index = NULL;
 	} else if (ovl_index_all(dentry->d_sb)) {
 		/* Whiteout orphan index to block future open by handle */
-		err = ovl_cleanup_and_whiteout(indexdir, dir, index);
+		err = ovl_cleanup_and_whiteout(ofs, indexdir, dir, index);
 	} else {
 		/* Cleanup orphan index entries */
 		err = ovl_cleanup(dir, index);
-- 
2.20.1






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