linux-kernel - Re: Massive slowdown when re-querying large nfs dir

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Message-Id: <20071108010436.e5ad5036.akpm@linux-foundation.org>
Date:	Thu, 8 Nov 2007 01:04:36 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Al Boldi <a1426z@...ab.com>
Cc:	neilb@...e.de, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: Massive slowdown when re-querying large nfs dir

> On Thu, 8 Nov 2007 10:44:35 +0300 Al Boldi <a1426z@...ab.com> wrote:
> Andrew Morton wrote:
> > > > I would suggest getting a 'tcpdump -s0' trace and seeing (with
> > > > wireshark) what is different between the various cases.
> > >
> > > Thanks Neil for looking into this.  Your suggestion has already been
> > > answered in a previous post, where the difference has been attributed to
> > > "ls -l" inducing lookup for the first try, which is fast, and getattr
> > > for later tries, which is super-slow.
> > >
> > > Now it's easy to blame the userland rpc.nfs.V2 server for this, but
> > > what's not clear is how come 2.4.31 handles getattr faster than 2.6.23?
> >
> > We broke 2.6?  It'd be interesting to run the ls in an infinite loop on
> > the client them start poking at the server.  Is the 2.6 server doing
> > physical IO?  Is the 2.6 server consuming more system time?  etc.  A basic
> > `vmstat 1' trace for both 2.4 and 2.6 would be a starting point.
> >
> > Could be that there's some additional latency caused by networking
> > changes, too.  I expect the tcpdump/wireshark/etc traces would have
> > sufficient resolution for us to be able to see that.
> 
> The problem turns out to be "tune2fs -O dir_index".
> Removing that feature resolves the big slowdown.

Doh.  Well worked-out.

> Does 2.4.31 support this feature?

No.  This explains it.
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