From mboxrd@z Thu Jan 1 00:00:00 1970 From: "J. R. Okajima" Subject: vfs-scale, general questions (Re: NFS root lockups with -next 20110113) Date: Wed, 19 Jan 2011 15:43:03 +0900 Message-ID: <909.1295419383@jrobl> References: <20110113120626.GB30351@opensource.wolfsonmicro.com> <8138.1294924927@jrobl> <676f5c24375e1cc2aa14fe6630ef1324@mail.gmail.com> <8482.1294926315@jrobl> Cc: Santosh Shilimkar , Mark Brown , Trond Myklebust , Nick Piggin , linux-nfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Nick Piggin Return-path: In-Reply-To: Sender: linux-nfs-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-fsdevel.vger.kernel.org Hi, Nick Piggin: > Thanks for your help, can you see how I've fixed it in my vfs-scale > tree? What do you think? Your fix is great. I have no objection at all. Other than the fix, here are more generic questions about vfs-scale work. I am happy if you reply when you have time. - getcwd(2) needs d_lock? It acquires rename_lock and then tests whether the pwd is removed by d_unhashed(). If a race condition between vfs_rename_dir() which may unhash/rehash the dentry happens, then getcwd() may return the wrong result due to unprotected d_unhashed() call, I am afraid. rename_lock doesn't help this case. - what is the right order of dget() and mntget()? If I remember correctly, someone said "mntget() first and then dget(). when putting, do in reverse" in the discussion when path_{get,put}() were born. So it is called "the right order" in the commit log. It was many years ago. Is it still true? And should rcu-walk follow it too? The current implementation doesn't seem to care about this order. - d_move() and rename_lock This may be out of rcu-walk work, but rename_lock in d_move() looks outstanding since it surely kills concurrency. It is a pity that two unrelated but concurrent d_move-s are serialized when we run rename(2) on two different filesystems. Even if all of dentries, parents and hash buckets are different from each other, d_move() never run concurrently. J. R. Okajima -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html