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    SubjectRe: [PATCH] remove sb->s_files and file_list_lock usage in dquot.c
    On Tue 06-02-07 15:50:01, Andrew Morton wrote:
    > On Tue, 6 Feb 2007 14:23:33 +0100
    > Christoph Hellwig <hch@lst.de> wrote:
    >
    > > 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);
    > > }
    >
    > That loop has (and had) up to O(n^n) operations. Is there something which
    > prevents this from going insane?
    Huh, I guess you meant O(n^2)... Yes, I know about this but as Christoph
    pointed out, the loop runs only when quotaon is called on a filesystem and for
    inodes somebody writes to. Usually, there are not so many such inodes. So
    I'm not sure it's worth the trouble to fix this.

    Honza
    --
    Jan Kara <jack@suse.cz>
    SuSE CR Labs
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