Re: 21 million inodes is causing severe pauses.

[Robin Holt <holt@sgi.com>]

On Mon, Nov 15, 2004 at 02:57:14PM -0800, Andrew Morton wrote:
> Robin Holt <holt@sgi.com> wrote:
> >
> > One significant problem we are running into is autofs trying to umount the
> > file systems.  This results in the umount grabbing the BKL and inode_lock,
> > holding it while it scans through the inode_list and others looking for
> > inodes used by this super block and attempting to free them.
> 
> You'll need invalidate_inodes-speedup.patch and
> break-latency-in-invalidate_list.patch (or an equivalent).
> 

I added the break-latency-in-invalidate_list.patch to the SLES9 kernel.
I am running the test again, but do not see how that change can do anything
to eliminate the race condition which appears to leave me with a NULL
pointer.  I will dig into that more today if other obligations allow it.

> That'll get you most of the way, but the BKL will still be a problem.
> 
> Removing lock_kernel() in the umount path is probably a major project so
> for now, you can just drop and reacquire it by doing
> release_kernel_lock()/reacquire_kernel_lock() around invalidate_inodes().

I guess I am very concerned at this point.  If I can do a
release/reacquire, why not just change generic_shutdown_super() so the
lock_kernel() does not happen until the first pass has occurred.  ie:

--- super.c.orig        2004-11-16 10:22:17 -06:00
+++ super.c     2004-11-16 10:22:41 -06:00
@@ -232,10 +232,10 @@
                dput(root);
                fsync_super(sb);
                lock_super(sb);
-               lock_kernel();
                sb->s_flags &= ~MS_ACTIVE;
                /* bad name - it should be evict_inodes() */
                invalidate_inodes(sb);
+               lock_kernel();

                if (sop->write_super && sb->s_dirt)
                        sop->write_super(sb);

This at least makes the lock_kernel time much smaller than it is right
now.  It also does not affect any callers that may really need the BKL.


I guess I am really asking for an indication of what the BKL is supposed
to be protecting.  I have not dug for the intent down the VFS code paths
at all.