linux-kernel - Re: [Patch] VFS : mount lock scalability for files systems without mount point (WAS vfsmount lock issues on very large ppc64 box)

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Message-ID: <20110723132411.GA22183@infradead.org>
Date:	Sat, 23 Jul 2011 09:24:11 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Tim Chen <tim.c.chen@...ux.intel.com>
Cc:	Al Viro <viro@...IV.linux.org.uk>,
	Christoph Hellwig <hch@...radead.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Andi Kleen <andi@...stfloor.org>,
	Matthew Wilcox <matthew@....cx>,
	Anton Blanchard <anton@...ba.org>, npiggin@...nel.dk,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [Patch] VFS : mount lock scalability for files systems without
 mount point   (WAS vfsmount lock issues on very large ppc64 box)

I think you actually want this done in kern_mount_data, as both
ipc and proc want long-term references as well.  I also suspect with
additional creep of container awareness more internal mounts will switch
to kern_mount_data.  Al, what do you think about simply passing the
private data argument to kern_mount and kill kern_mount_data?  It's not
like the additional argument is going to cause us any pain.

> +struct vfsmount *kern_mount(struct file_system_type *type)
> +{
> +	struct vfsmount *mnt;
> +
> +	mnt = kern_mount_data(type, NULL);
> +	if (!IS_ERR(mnt)) {
> +		/* it is a longterm mount, don't release mnt until */
> +		/* we unmount before file sys is unregistered */

Please use normal kernel comment style, e.g.

	/*
	 * This is a longterm mount, don't release mnt until we umount
	 * it just before unregister_filesystem().
	 */

Adding proper kerneldoc comments for the kern_mount/umount function that
explain things in more detail would also be nice.

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