vfs: dont chain pipe/anon/socket on superblock s_inodes list

Workloads using pipes and sockets hit inode_sb_list_lock contention.

superblock s_inodes list is needed for quota, dirty, pagecache and
fsnotify management. pipe/anon/socket fs are clearly not candidates for
these.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 30 insertions, 9 deletions

diff --git a/fs/inode.c b/fs/inode.c
index 96c77b81167c..319b93b55570 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -362,9 +362,11 @@ EXPORT_SYMBOL_GPL(inode_sb_list_add);
 
 static inline void inode_sb_list_del(struct inode *inode)
 {
-        spin_lock(&inode_sb_list_lock);
-        list_del_init(&inode->i_sb_list);
-        spin_unlock(&inode_sb_list_lock);
+        if (!list_empty(&inode->i_sb_list)) {
+                spin_lock(&inode_sb_list_lock);
+                list_del_init(&inode->i_sb_list);
+                spin_unlock(&inode_sb_list_lock);
+        }
 }
 
 static unsigned long hash(struct super_block *sb, unsigned long hashval)
@@ -797,6 +799,29 @@ unsigned int get_next_ino(void)
 EXPORT_SYMBOL(get_next_ino);
 
 /**
+ *      new_inode_pseudo        - obtain an inode
+ *      @sb: superblock
+ *
+ *      Allocates a new inode for given superblock.
+ *      Inode wont be chained in superblock s_inodes list
+ *      This means :
+ *      - fs can't be unmount
+ *      - quotas, fsnotify, writeback can't work
+ */
+struct inode *new_inode_pseudo(struct super_block *sb)
+{
+        struct inode *inode = alloc_inode(sb);
+
+        if (inode) {
+                spin_lock(&inode->i_lock);
+                inode->i_state = 0;
+                spin_unlock(&inode->i_lock);
+                INIT_LIST_HEAD(&inode->i_sb_list);
+        }
+        return inode;
+}
+
+/**
  *      new_inode       - obtain an inode
  *      @sb: superblock
  *
@@ -814,13 +839,9 @@ struct inode *new_inode(struct super_block *sb)
 
         spin_lock_prefetch(&inode_sb_list_lock);
 
-        inode = alloc_inode(sb);
-        if (inode) {
-                spin_lock(&inode->i_lock);
-                inode->i_state = 0;
-                spin_unlock(&inode->i_lock);
+        inode = new_inode_pseudo(sb);
+        if (inode)
                 inode_sb_list_add(inode);
-        }
         return inode;
 }
 EXPORT_SYMBOL(new_inode);