From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752005AbbE0J2o (ORCPT ); Wed, 27 May 2015 05:28:44 -0400 Received: from hofr.at ([212.69.189.236]:59449 "EHLO mail.hofr.at" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751233AbbE0J2m (ORCPT ); Wed, 27 May 2015 05:28:42 -0400 Date: Wed, 27 May 2015 11:28:39 +0200 From: Nicholas Mc Guire To: Linus Torvalds Cc: Davidlohr Bueso , Peter Zijlstra , Oleg Nesterov , Paul McKenney , Tejun Heo , Ingo Molnar , Linux Kernel Mailing List Subject: Re: [RFC][PATCH 0/5] Optimize percpu-rwsem Message-ID: <20150527092839.GA12011@opentech.at> References: <20150526114356.609107918@infradead.org> <1432665731.8196.3.camel@stgolabs.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 26 May 2015, Linus Torvalds wrote: > On Tue, May 26, 2015 at 11:42 AM, Davidlohr Bueso wrote: > > > > Instead of dropping percpu-rwsem, I was thinking we could instead look > > for opportunities to convert new users, for instance shinkers, where the > > write lock is also taken just for register and unregister purposes, > > similar to uprobes. > > So if there really are useful use cases for this, I don't object to > the patch. It seems to just improve on a currently very low-usage > locking primitive. > > And it's not like I conceptually mind the notion of a percpu rwsem, I > just hate seeing specialty locking that isn't really worth it. > > Because as it is, with the current single use, I don't think it's even > worth improving on. > > I _would_ ask that people who are looking at this also look at our > "lglock" thing. It's pretty much *exactly* the same thing, except for > spinlocks, and that one too has exactly two users (the documentation > states that the only user is stop_machine, but in fact file locking > does too). > not sure where this would be missing: Documentation/locking/lglock.txt "Users: currently only the VFS and stop_machine related code" I atleast did not find any other users as of 3.18 and in 4.0-rc5 this still seems valid. thx! hofrat