linux-kernel - Re: getting rid of filp search in fs_may_remount

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Date:	Wed, 2 Jan 2008 21:33:57 +0100
From:	Christoph Hellwig <hch@....de>
To:	Dave Hansen <haveblue@...ibm.com>
Cc:	Christoph Hellwig <hch@....de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: getting rid of filp search in fs_may_remount_ro()

On Mon, Dec 31, 2007 at 02:54:48PM -0800, Dave Hansen wrote:
> Here's one blatantly untested idea I have.  The idea is to keep track if
> anyone might be writing to a mnt.  We keep track on a flag in the mnt.
> When we set the flag, we increment a counter in the sb and decrement
> when the flag is cleared.
> 
> We can't simply look at mnt->__mnt_writers because there might be
> "checked-out" writers in the mnt_writers[] array.  We also have to keep
> new writers from coming in while we do this, so we use the spinlocks in
> the mnt_writers[] array for exclusion.  This is a pretty heavyweight
> lock, but it only gets used at rw->ro transitions.

This idea looks good to me, but if you're going to a final version
please just inline fs_may_remount_ro into its only caller.

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