[PATCH] remove sb->s_files and file_list_lock usage in dquot.c

Iterate over sb->s_inodes instead of sb->s_files in add_dquot_ref.  This
reduces list search and lock hold time aswell as getting rid of one of the
few uses of file_list_lock which Ingo identified as a scalability problem.

Previously we called dq_op->initialize for every inode handing of a
writeable file that wasn't initialized before.  Now we're calling it for
every inode that has a non-zero i_writecount, aka a writeable file
descriptor refering to it.

Thanks a lot to Jan Kara for running this patch through his quota test
harness.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 18 insertions, 14 deletions

diff --git a/fs/dquot.c b/fs/dquot.c
index 5bdc4b2a872a..9eb166f91489 100644
--- a/fs/dquot.c
+++ b/fs/dquot.c
@@ -688,23 +688,27 @@ static int dqinit_needed(struct inode *inode, int type)
 /* This routine is guarded by dqonoff_mutex mutex */
 static void add_dquot_ref(struct super_block *sb, int type)
 {
-        struct list_head *p;
+        struct inode *inode;
 
 restart:
-        file_list_lock();
-        list_for_each(p, &sb->s_files) {
-                struct file *filp = list_entry(p, struct file, f_u.fu_list);
-                struct inode *inode = filp->f_path.dentry->d_inode;
-                if (filp->f_mode & FMODE_WRITE && dqinit_needed(inode, type)) {
-                        struct dentry *dentry = dget(filp->f_path.dentry);
-                        file_list_unlock();
-                        sb->dq_op->initialize(inode, type);
-                        dput(dentry);
-                        /* As we may have blocked we had better restart... */
-                        goto restart;
-                }
+        spin_lock(&inode_lock);
+        list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
+                if (!atomic_read(&inode->i_writecount))
+                        continue;
+                if (!dqinit_needed(inode, type))
+                        continue;
+                if (inode->i_state & (I_FREEING|I_WILL_FREE))
+                        continue;
+
+                __iget(inode);
+                spin_unlock(&inode_lock);
+
+                sb->dq_op->initialize(inode, type);
+                iput(inode);
+                /* As we may have blocked we had better restart... */
+                goto restart;
         }
-        file_list_unlock();
+        spin_unlock(&inode_lock);
 }
 
 /* Return 0 if dqput() won't block (note that 1 doesn't necessarily mean blocking) */