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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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      Last update: 2007-02-06 14:27    [W:0.022 / U:0.148 seconds]
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