linux-kernel - Re: [PATCH 3/6] autofs4: allow RCU-walk to walk through autofs4.

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Date:	Thu, 17 Jul 2014 13:00:56 +0800
From:	Ian Kent <raven@...maw.net>
To:	NeilBrown <neilb@...e.de>
Cc:	autofs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/6] autofs4: allow RCU-walk to walk through autofs4.

On Wed, 2014-07-16 at 14:56 +0800, Ian Kent wrote:
> > That looks a bit messy ... I wonder if we could have a new "ino" flag which
> > says "This dentry is mounted-on if it needs to be.  Gets set by ->lookup
> > and cleared by ->d_automount or when ->d_manage returns -EISDIR.
> 
> At one point DCACHE_NEED_AUTOMOUNT and DCACHE_MANAGE_TRANSIT were
> handled separately and DCACHE_NEED_AUTOMOUNT was cleared for rootless
> multi-mount dentrys following a mount and set again at expire. Not
> having to worry about managing that flag was also part of the
> optimization.
> 
> We could go back to managing DCACHE_NEED_AUTOMOUNT or add a new flag.
> I'm not fussy how it's done as long as it works. IIRC there was one
> quite convoluted if check (in the expire code) that was removed due to
> the optimization.

Umm ... using DCACHE_NEED_AUTOMOUNT rather than a new flag means using
an additional lock so perhaps a new flag would be preferred since
reducing lock overhead was the point of this.

Just a thought
Ian

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