From: Anand Avati <anand.avati-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Subject: Re: regressions due to 64-bit ext4 directory cookies
Date: Thu, 28 Mar 2013 11:49:36 -0700
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Cc: Eric Sandeen <sandeen-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, linux-nfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	Theodore Ts'o <tytso-3s7WtUTddSA@public.gmane.org>, Zach Brown <zab-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
	Bernd Schubert <bernd.schubert-mPn0NPGs4xGatNDF+KUbs4QuADTiUCJX@public.gmane.org>,
	linux-ext4-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, gluster-devel-qX2TKyscuCcdnm+yROfE0A@public.gmane.org
To: "J. Bruce Fields" <bfields-uC3wQj2KruNg9hUCZPvPmw@public.gmane.org>
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On Thu, Mar 28, 2013 at 11:31 AM, J. Bruce Fields <bfields-uC3wQj2KruNg9hUCZPvPmw@public.gmane.org>wrote:
>
> > Jeff reported that the approach did not work in his testing. I haven't
> had
> > a chance to look into the failure yet. Independent of the fix, it would
> > certainly be good have the ioctl() support
>
> The one advantage of your scheme is that it keeps more of the hash bits;
> the chance of 31-bit cookie collisions is much higher.


Yes, it should, based on the theory of how ext4 was generating the 63bits.
But Jeff's test finds that the experiment is not matching the theory. I
intend to debug this, but currently drowned in a different issue. It would
be good if the ext developers can have a look at
http://review.gluster.org/4711 and see if there are obvious holes in the
approach or code.

Avati

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<br><br><div class=3D"gmail_quote">On Thu, Mar 28, 2013 at 11:31 AM, J. Bru=
ce Fields <span dir=3D"ltr">&lt;<a href=3D"mailto:bfields-uC3wQj2KruNg9hUCZPvPmw@public.gmane.org" tar=
get=3D"_blank">bfields-uC3wQj2KruNg9hUCZPvPmw@public.gmane.org</a>&gt;</span> wrote:<blockquote class=
=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padd=
ing-left:1ex">
<div class=3D"HOEnZb"><div class=3D"h5">
&gt; Jeff reported that the approach did not work in his testing. I haven&#=
39;t had<br>
&gt; a chance to look into the failure yet. Independent of the fix, it woul=
d<br>
&gt; certainly be good have the ioctl() support<br>
<br>
</div></div>The one advantage of your scheme is that it keeps more of the h=
ash bits;<br>
the chance of 31-bit cookie collisions is much higher.</blockquote><div><br=
></div><div>Yes, it should, based on the theory of how ext4 was generating =
the 63bits. But Jeff&#39;s test finds that the experiment is not matching t=
he theory. I intend to debug this, but currently drowned in a different iss=
ue. It would be good if the ext developers can have a look at <a href=3D"ht=
tp://review.gluster.org/4711">http://review.gluster.org/4711</a> and see if=
 there are obvious holes in the approach or code.</div>
<div><br></div><div>Avati</div><div><br></div></div>

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