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Subject[PATCH 12/13] vfs: count unlinked inodes
Date
From: Miklos Szeredi <mszeredi@suse.cz>

Add a new counter to the superblock that keeps track of unlinked but
not yet deleted inodes.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---
fs/inode.c | 81 ++++++++++++++++++++++++++++++++++++++++++++++++++++
include/linux/fs.h | 61 ++++----------------------------------
2 files changed, 88 insertions(+), 54 deletions(-)

diff --git a/fs/inode.c b/fs/inode.c
index e2d3633..ca27d4e 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -241,6 +241,11 @@ void __destroy_inode(struct inode *inode)
BUG_ON(inode_has_buffers(inode));
security_inode_free(inode);
fsnotify_inode_delete(inode);
+ if (!inode->i_nlink) {
+ WARN_ON(atomic_long_read(&inode->i_sb->s_remove_count) == 0);
+ atomic_long_dec(&inode->i_sb->s_remove_count);
+ }
+
#ifdef CONFIG_FS_POSIX_ACL
if (inode->i_acl && inode->i_acl != ACL_NOT_CACHED)
posix_acl_release(inode->i_acl);
@@ -268,6 +273,82 @@ static void destroy_inode(struct inode *inode)
call_rcu(&inode->i_rcu, i_callback);
}

+/**
+ * drop_nlink - directly drop an inode's link count
+ * @inode: inode
+ *
+ * This is a low-level filesystem helper to replace any
+ * direct filesystem manipulation of i_nlink. In cases
+ * where we are attempting to track writes to the
+ * filesystem, a decrement to zero means an imminent
+ * write when the file is truncated and actually unlinked
+ * on the filesystem.
+ */
+void drop_nlink(struct inode *inode)
+{
+ WARN_ON(inode->i_nlink == 0);
+ inode->__i_nlink--;
+ if (!inode->i_nlink)
+ atomic_long_inc(&inode->i_sb->s_remove_count);
+}
+EXPORT_SYMBOL(drop_nlink);
+
+/**
+ * clear_nlink - directly zero an inode's link count
+ * @inode: inode
+ *
+ * This is a low-level filesystem helper to replace any
+ * direct filesystem manipulation of i_nlink. See
+ * drop_nlink() for why we care about i_nlink hitting zero.
+ */
+void clear_nlink(struct inode *inode)
+{
+ if (inode->i_nlink) {
+ inode->__i_nlink = 0;
+ atomic_long_inc(&inode->i_sb->s_remove_count);
+ }
+}
+EXPORT_SYMBOL(clear_nlink);
+
+/**
+ * set_nlink - directly set an inode's link count
+ * @inode: inode
+ * @nlink: new nlink (should be non-zero)
+ *
+ * This is a low-level filesystem helper to replace any
+ * direct filesystem manipulation of i_nlink.
+ */
+void set_nlink(struct inode *inode, unsigned int nlink)
+{
+ if (WARN_ON(!nlink)) {
+ clear_nlink(inode);
+ } else {
+ /* Yes, some filesystems do change nlink from zero to one */
+ if (inode->i_nlink == 0)
+ atomic_long_dec(&inode->i_sb->s_remove_count);
+
+ inode->__i_nlink = nlink;
+ }
+}
+EXPORT_SYMBOL(set_nlink);
+
+/**
+ * inc_nlink - directly increment an inode's link count
+ * @inode: inode
+ *
+ * This is a low-level filesystem helper to replace any
+ * direct filesystem manipulation of i_nlink. Currently,
+ * it is only here for parity with dec_nlink().
+ */
+void inc_nlink(struct inode *inode)
+{
+ if (WARN_ON(inode->i_nlink == 0))
+ atomic_long_dec(&inode->i_sb->s_remove_count);
+
+ inode->__i_nlink++;
+}
+EXPORT_SYMBOL(inc_nlink);
+
void address_space_init_once(struct address_space *mapping)
{
memset(mapping, 0, sizeof(*mapping));
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 7813404..71bacce 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1473,6 +1473,9 @@ struct super_block {

struct shrinker s_shrink; /* per-sb shrinker handle */

+ /* Number of inodes with nlink == 0 but still referenced */
+ atomic_long_t s_remove_count;
+
/* Being remounted read-only */
int s_readonly_remount;
};
@@ -1757,31 +1760,10 @@ static inline void mark_inode_dirty_sync(struct inode *inode)
__mark_inode_dirty(inode, I_DIRTY_SYNC);
}

-/**
- * set_nlink - directly set an inode's link count
- * @inode: inode
- * @nlink: new nlink (should be non-zero)
- *
- * This is a low-level filesystem helper to replace any
- * direct filesystem manipulation of i_nlink.
- */
-static inline void set_nlink(struct inode *inode, unsigned int nlink)
-{
- inode->__i_nlink = nlink;
-}
-
-/**
- * inc_nlink - directly increment an inode's link count
- * @inode: inode
- *
- * This is a low-level filesystem helper to replace any
- * direct filesystem manipulation of i_nlink. Currently,
- * it is only here for parity with dec_nlink().
- */
-static inline void inc_nlink(struct inode *inode)
-{
- inode->__i_nlink++;
-}
+extern void inc_nlink(struct inode *inode);
+extern void drop_nlink(struct inode *inode);
+extern void clear_nlink(struct inode *inode);
+extern void set_nlink(struct inode *inode, unsigned int nlink);

static inline void inode_inc_link_count(struct inode *inode)
{
@@ -1789,35 +1771,6 @@ static inline void inode_inc_link_count(struct inode *inode)
mark_inode_dirty(inode);
}

-/**
- * drop_nlink - directly drop an inode's link count
- * @inode: inode
- *
- * This is a low-level filesystem helper to replace any
- * direct filesystem manipulation of i_nlink. In cases
- * where we are attempting to track writes to the
- * filesystem, a decrement to zero means an imminent
- * write when the file is truncated and actually unlinked
- * on the filesystem.
- */
-static inline void drop_nlink(struct inode *inode)
-{
- inode->__i_nlink--;
-}
-
-/**
- * clear_nlink - directly zero an inode's link count
- * @inode: inode
- *
- * This is a low-level filesystem helper to replace any
- * direct filesystem manipulation of i_nlink. See
- * drop_nlink() for why we care about i_nlink hitting zero.
- */
-static inline void clear_nlink(struct inode *inode)
-{
- inode->__i_nlink = 0;
-}
-
static inline void inode_dec_link_count(struct inode *inode)
{
drop_nlink(inode);
--
1.7.3.4


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