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Date: Tue, 10 Sep 2013 01:57:54 +0100
From: Al Viro <viro@ZenIV.linux.org.uk>
To: George Spelvin <linux@horizon.com>
Cc: torvalds@linux-foundation.org, aswin@hp.com, john@stoffel.org,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        scott.norton@hp.com, Waiman.Long@hp.com
Subject: Re: [PATCH v4 1/1] dcache: Translating dentry into pathname without
 taking rename_lock
Message-ID: <20130910005754.GV13318@ZenIV.linux.org.uk>
References: <20130909182111.GQ13318@ZenIV.linux.org.uk>
 <20130910004020.29299.qmail@science.horizon.com>
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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.