From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kara Subject: Re: [PATCH] remove sb->s_files and file_list_lock usage in dquot.c Date: Wed, 7 Feb 2007 09:35:57 +0100 Message-ID: <20070207083557.GA5192@duck.suse.cz> References: <20070206132333.GA9919@lst.de> <20070206155001.22ab74f6.akpm@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Christoph Hellwig , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org To: Andrew Morton Return-path: Content-Disposition: inline In-Reply-To: <20070206155001.22ab74f6.akpm@linux-foundation.org> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Tue 06-02-07 15:50:01, Andrew Morton wrote: > On Tue, 6 Feb 2007 14:23:33 +0100 > Christoph Hellwig 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 SuSE CR Labs