linux-kernel - Re: [PATCH] doc/rcu: Correct field

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Message-Id: <20190514221332.GC4184@linux.ibm.com>
Date:   Tue, 14 May 2019 15:13:32 -0700
From:   "Paul E. McKenney" <paulmck@...ux.ibm.com>
To:     Joel Fernandes <joel@...lfernandes.org>
Cc:     linux-kernel@...r.kernel.org, rcu@...r.kernel.org,
        Josh Triplett <josh@...htriplett.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Andrea Parri <andrea.parri@...rulasolutions.com>,
        Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org
Subject: Re: [PATCH] doc/rcu: Correct field_count field naming in examples

On Sun, May 12, 2019 at 11:43:05PM -0400, Joel Fernandes wrote:
> On Wed, May 08, 2019 at 11:16:38AM -0700, Paul E. McKenney wrote:
> [snip]
> > > The other example could be dentry look up which uses seqlocks for the
> > > RCU-walk case? But that could be too complex. This is also something I first
> > > learnt from the paper and then the excellent path-lookup.rst document in
> > > kernel sources.
> > 
> > This is a great example, but it would need serious simplification for
> > use in the Documentation/RCU directory.  Note that dcache uses it to
> > gain very limited and targeted consistency -- only a few types of updates
> > acquire the write-side of that seqlock.
> > 
> > Might be quite worthwhile to have a simplified example, though!
> > Perhaps a trivial hash table where write-side sequence lock is acquired
> > only when moving an element from one chain to another?
> 
> Here you meant "moving from one chain to another" in the case of
> hashtable-resizing right? I could not think of another reason why an element
> is moved between 2 hash chains.

Either that or in terms of atomic rekeying of a specific element in that
table, thus potentially requiring an atomic move of only that specific
element to another hash chain.

> I just finished reading the main parts of Josh's relativistic hashtable paper
> [1] and it is very cool indeed. The whole wait-for-readers application for
> hashtable expansion is so well thought. I am planning to go over more papers
> and code and can certainly update this example with a read-mostly hashtable
> example as well as you are suggesting. :-)
> 
> [1] https://www.usenix.org/legacy/event/atc11/tech/final_files/Triplett.pdf

Sounds very good!

							Thanx, Paul