Re: [PATCH 14/17] prmem: llist, hlist, both plain and rcu

From: Peter Zijlstra
Date: Fri Oct 26 2018 - 05:57:27 EST

On Wed, Oct 24, 2018 at 12:35:01AM +0300, Igor Stoppa wrote:
> In some cases, all the data needing protection can be allocated from a pool
> in one go, as directly writable, then initialized and protected.
> The sequence is relatively short and it's acceptable to leave the entire
> data set unprotected.
> In other cases, this is not possible, because the data will trickle over
> a relatively long period of time, in a non predictable way, possibly for
> the entire duration of the operations.
> For these cases, the safe approach is to have the memory already write
> protected, when allocated. However, this will require replacing any
> direct assignment with calls to functions that can perform write rare.
> Since lists are one of the most commonly used data structures in kernel,
> they are a the first candidate for receiving write rare extensions.
> This patch implements basic functionality for altering said lists.
> Signed-off-by: Igor Stoppa <igor.stoppa@xxxxxxxxxx>
> CC: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> CC: Kate Stewart <kstewart@xxxxxxxxxxxxxxxxxxx>
> CC: "David S. Miller" <davem@xxxxxxxxxxxxx>
> CC: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> CC: Philippe Ombredanne <pombredanne@xxxxxxxx>
> CC: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
> CC: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
> CC: Steven Rostedt <rostedt@xxxxxxxxxxx>
> CC: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
> CC: Lai Jiangshan <jiangshanlai@xxxxxxxxx>
> CC: linux-kernel@xxxxxxxxxxxxxxx
> ---
> include/linux/prlist.h | 934 +++++++++++++++++++++++++++++++++++++++++

I'm not at all sure I understand the Changelog, or how it justifies
duplicating almost 1k lines of code.

Sure lists aren't the most complicated thing we have, but duplicating
that much is still very _very_ bad form. Why are we doing this?