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Subject[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.

Note: this is ontop of '[PATCH] move remove_dquot_ref to dqout.c'
which I sent out yesterday.


Signed-off-by: Christoph Hellwig <hch@lst.de>

Index: linux-2.6/fs/dquot.c
===================================================================
--- linux-2.6.orig/fs/dquot.c 2007-02-05 18:54:36.000000000 +0100
+++ linux-2.6/fs/dquot.c 2007-02-05 18:59:48.000000000 +0100
@@ -689,23 +689,27 @@
/* 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) */
-
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