linux-kernel - Re: [PATCH] fs/locks.c: prepare for BKL removal

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Date:	Sat, 18 Sep 2010 07:48:20 -0600
From:	Matthew Wilcox <matthew@....cx>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-kernel@...r.kernel.org,
	Matthew Wilcox <willy@...ux.intel.com>,
	Christoph Hellwig <hch@....de>,
	Trond Myklebust <trond.myklebust@....uio.no>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Miklos Szeredi <mszeredi@...e.cz>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>, John Kacur <jkacur@...hat.com>,
	Sage Weil <sage@...dream.net>, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] fs/locks.c: prepare for BKL removal

On Sat, Sep 18, 2010 at 03:09:31PM +0200, Arnd Bergmann wrote:
> This prepares the removal of the big kernel lock from the
> file locking code. We still use the BKL as long as fs/lockd
> uses it and ceph might sleep, but we can flip the definition
> to a private spinlock as soon as that's done.
> All users outside of fs/lockd get converted to use
> lock_flocks() instead of lock_kernel() where appropriate.
> 
> Based on an earlier patch to use a spinlock from Matthew
> Wilcox, who has attempted this a few times before. An even
> earlier attempt to use a semaphore instead of the BKL
> apparently was made by Andrew Morton about ten years ago,
> but reverted for performance reasons.

Actually, I attempted the semaphore conversion ten years ago, but Andrew
Morton reverted it due to the performance regression.  I believe it was
Apache, when it was using file locks to synchronise between threads.

Patch looks good; Acked-by: Matthew Wilcox <willy@...ux.intel.com>

-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."
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