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SubjectRe: 21 million inodes is causing severe pauses.
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.
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