linux-kernel - Re: [PATCH v4 1/1] dcache: Translating dentry into pathname without taking rename

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Message-ID: <20130910005754.GV13318@ZenIV.linux.org.uk>
Date:	Tue, 10 Sep 2013 01:57:54 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	George Spelvin <linux@...izon.com>
Cc:	torvalds@...ux-foundation.org, aswin@...com, john@...ffel.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	scott.norton@...com, Waiman.Long@...com
Subject: Re: [PATCH v4 1/1] dcache: Translating dentry into pathname without
 taking rename_lock

On Mon, Sep 09, 2013 at 08:40:20PM -0400, George Spelvin wrote:
> I'm really wondering about only trying once before taking the write lock.
> Yes, using the lsbit is a cute hack, but are we using it for its cuteness
> rather than its effectiveness?
> 
> Renames happen occasionally.  If that causes all the current pathname
> translations to fall back to the write lock, that is fairly heavy.
> Worse, all of those translations will (unnecessarily) bump the write
> seqcount, triggering *other* translations to fail back to the write-lock
> path.

_What_ "pathname translations"?  Pathname resolution doesn't fall back to
seq_writelock() at all.
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