From mboxrd@z Thu Jan  1 00:00:00 1970
Date: Fri, 8 Jun 2012 23:23:37 +0100
From: Al Viro <viro@ZenIV.linux.org.uk>
To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [RFC, PATCH, RESEND] fs: push rcu_barrier() from
 deactivate_locked_super() to filesystems
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On Sat, Jun 09, 2012 at 01:14:46AM +0300, Kirill A. Shutemov wrote:
> > The implementation would be less unpleasant if we could do the
> > rcu_barrier() in kmem_cache_destroy().  I can't see a way of doing that
> > without adding a dedicated slab flag, which would require editing all
> > the filesystems anyway.
> 
> I think rcu_barrier() for all kmem_cache_destroy() would be too expensive.

You've got to be kidding.  Please, show us the codepath that would be hot
enough to make that too expensive and would contain kmem_cache_destroy().
Note that module unload is *not* a hot path - not on any even remotely sane
use.