From: Christoph Hellwig <hch@infradead.org>
To: Dave Hansen <haveblue@us.ibm.com>
Cc: viro@ftp.linux.org.uk, hch@infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] r/o bind mounts: add vfsmount and superblock writer counts
Date: Tue, 9 Jan 2007 10:53:05 +0000 [thread overview]
Message-ID: <20070109105305.GA22984@infradead.org> (raw)
In-Reply-To: <20070108183445.9472D522@localhost.localdomain>
On Mon, Jan 08, 2007 at 10:34:45AM -0800, Dave Hansen wrote:
> Removing it had a few side-effects. First of all, it made me move
> all of the operations on the counts of writers to underneath the
> spinlock that was already there. I guess this could be a cause
> for potential contention because there _are_ locks in the common
> code paths now. But, I do agree with Christoph that it would be
> awfully hard to get it contended.
>
> The other side-effect is that we can't have the bit in mnt_flags
> to be a shortcut to the superblock's writeable state since we
> don't have a way to go find the mounts and that bit when a fs
> changes writeable state. This causes a potential cache miss
> when we have to check the superblock directly during the
> relatively common __mnt_is_readonly() function.
Why? We _only_ need to check the vfsmount flag. vfsmount can
become r/w if the superblock is marked r/o which means the
underlying (block/network/etc) device is fundamentally not writeable.
next prev parent reply other threads:[~2007-01-09 10:53 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-01-08 18:34 [PATCH] r/o bind mounts: add vfsmount and superblock writer counts Dave Hansen
2007-01-09 10:53 ` Christoph Hellwig [this message]
2007-01-10 18:33 ` Dave Hansen
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