linux-kernel - Re: [PATCH 00/20] staging: lustre: convert to rhashtable

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Date:   Mon, 23 Apr 2018 15:08:37 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     NeilBrown <neilb@...e.com>
Cc:     Oleg Drokin <oleg.drokin@...el.com>,
        James Simmons <jsimmons@...radead.org>,
        Andreas Dilger <andreas.dilger@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Lustre Development List <lustre-devel@...ts.lustre.org>
Subject: Re: [PATCH 00/20] staging: lustre: convert to rhashtable

On Thu, Apr 12, 2018 at 07:54:48AM +1000, NeilBrown wrote:
> libcfs in lustre has a resizeable hashtable.
> Linux already has a resizeable hashtable, rhashtable, which is better
> is most metrics. See https://lwn.net/Articles/751374/ in a few days
> for an introduction to rhashtable.
> 
> This series converts lustre to use rhashtable.  This affects several
> different tables, and each is different is various ways.
> 
> There are two outstanding issues.  One is that a bug in rhashtable
> means that we cannot enable auto-shrinking in one of the tables.  That
> is documented as appropriate and should be fixed soon.
> 
> The other is that rhashtable has an atomic_t which counts the elements
> in a hash table.  At least one table in lustre went to some trouble to
> avoid any table-wide atomics, so that could lead to a regression.
> I'm hoping that rhashtable can be enhanced with the option of a
> per-cpu counter, or similar.
> 
> 
> I have enabled automatic shrinking on all tables where it makes sense
> and doesn't trigger the bug.  I have also removed all hints concerning
> min/max size - I cannot see how these could be useful.
> 
> The dump_pgcache debugfs file provided some interesting challenges.  I
> think I have cleaned it up enough so that it all makes sense.  An
> extra pair of eyes examining that code in particular would be
> appreciated.
> 
> This series passes all the same tests that pass before the patches are
> applied.

I've taken the first 4 patches of this series, as they were "obviously
correct".  I'll let you and James argue about the rest.  Feel free to
resend when there's some sort of agreement.

thanks,

greg k-h