linux-ext4 - Re: [RFC, PATCH, RESEND] fs: push rcu_barrier() from deactivate_locked

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Message-ID: <20120608222337.GR30000@ZenIV.linux.org.uk>
Date:	Fri, 8 Jun 2012 23:23:37 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Boaz Harrosh <bharrosh@...asas.com>,
	Tao Ma <boyu.mt@...bao.com>, Nick Piggin <npiggin@...nel.dk>,
	"Dmitry V. Levin" <ldv@...linux.org>,
	v9fs-developer@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-afs@...ts.infradead.org,
	linux-btrfs@...r.kernel.org, ceph-devel@...r.kernel.org,
	linux-cifs@...r.kernel.org, samba-technical@...ts.samba.org,
	codalist@...EMANN.coda.cs.cmu.edu, ecryptfs@...r.kernel.org,
	osd-dev@...n-osd.org, linux-ext4@...r.kernel.org,
	fuse-devel@...ts.sourceforge.net, linux-mtd@...ts.infradead.org,
	jfs-discussion@...ts.sourceforge.net, logfs@...fs.org,
	linux-nfs@...r.kernel.org, linux-nilfs@...r.kernel.org,
	linux-ntfs-dev@...ts.sourceforge.net, ocfs2-devel@....oracle.com,
	reiserfs-devel@...r.kernel.org
Subject: Re: [RFC, PATCH, RESEND] fs: push rcu_barrier() from
 deactivate_locked_super() to filesystems

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.
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