From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-6.0 required=5.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=unavailable autolearn_force=no version=3.4.2 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id 60BD67D8A4 for ; Sat, 11 May 2019 22:11:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726099AbfEKWLi (ORCPT ); Sat, 11 May 2019 18:11:38 -0400 Received: from mail-wm1-f66.google.com ([209.85.128.66]:55087 "EHLO mail-wm1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726210AbfEKWLh (ORCPT ); Sat, 11 May 2019 18:11:37 -0400 Received: by mail-wm1-f66.google.com with SMTP id i3so4693874wml.4 for ; Sat, 11 May 2019 15:11:35 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amarulasolutions.com; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=d1+FGziLF47L4qrx03aVD+M8jY5l9sq1jNKrZJyhi2o=; b=Ej4E7gbnKGYiowwSnWtaTwbeMaxu1nIyXWrwEaork0CeI/aFXbuw4R6MmShvlH/OZ4 fC5MfKzqE6lg+eUSu+7ClEGLLRY+L/4hU+vlLfCpQZokJksy/FUSAezD1n3yQyBSXfWJ 5WDCkAW7BK2eq0YLIvZHkl87MGNWpVc+Id3/M= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=d1+FGziLF47L4qrx03aVD+M8jY5l9sq1jNKrZJyhi2o=; b=aewXqyAvEvPK6JZnQd6umnzJu/LfsHAFoo0kLAMNqdYhD9JsgL9jRyHDVvuGk3Dp+N TaOlIs7+eRroVgqe0a7x2XQs2rT2DtcrwTtk+EE98y6yfQKBFXgq4gPFWF3t9q94201y nUxJEmgzqVrMHUoU3mOzqimVhsNd8RmIxhM1SDcE+mNmkosryObeI4aGuK23Gq+2hAmy dTl8Is4NCJN9l2NqO3W2paorMu86lQHFZemdwci1TTeMZJdn+gdttFwnPJz7xQ6fXBR4 feU8RjKKzCD6XaARTM2gcRjDajZNnrt/8HUPQ2bMyohivUpAVMH/uLDVt+Vq2kTHICZ+ PJVg== X-Gm-Message-State: APjAAAUtdOtBw1OUggCgYyvc11tnqvayAB7nFPtQ1tc7b4QnleYgWbke /EVwx2sfXxd5vPAj8iiEtgcE5Q== X-Google-Smtp-Source: APXvYqxOKIy4AHjaZp8FltX2FkddcS0U5ptHUeNcdKRpT68Ku+qiK08plVhUjpP6TiWqvwmGdD4eYw== X-Received: by 2002:a1c:cc10:: with SMTP id h16mr11462278wmb.39.1557612695128; Sat, 11 May 2019 15:11:35 -0700 (PDT) Received: from andrea ([89.22.71.151]) by smtp.gmail.com with ESMTPSA id 91sm17491123wrs.43.2019.05.11.15.11.33 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sat, 11 May 2019 15:11:34 -0700 (PDT) Date: Sun, 12 May 2019 00:11:26 +0200 From: Andrea Parri To: "Paul E. McKenney" Cc: Joel Fernandes , linux-kernel@vger.kernel.org, rcu@vger.kernel.org, Josh Triplett , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Jonathan Corbet , linux-doc@vger.kernel.org Subject: Re: [PATCH] doc/rcu: Correct field_count field naming in examples Message-ID: <20190511221126.GA3984@andrea> References: <20190505020328.165839-1-joel@joelfernandes.org> <20190507000453.GB3923@linux.ibm.com> <20190508162635.GD187505@google.com> <20190508181638.GY3923@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190508181638.GY3923@linux.ibm.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org Hi Paul, Joel, > > > On the other hand, would you have ideas for more modern replacement > > > examples? > > > > There are 3 cases I can see in listRCU.txt: > > (1) action taken outside of read_lock (can tolerate stale data), no in-place update. > > this is the best possible usage of RCU. > > (2) action taken outside of read_lock, in-place updates > > this is good as long as not too many in-place updates. > > involves copying creating new list node and replacing the > > node being updated with it. > > (3) cannot tolerate stale data: here a deleted or obsolete flag can be used > > protected by a per-entry lock. reader > > aborts if object is stale. > > > > Any replacement example must make satisfy (3) too? > > It would be OK to have a separate example for (3). It would of course > be nicer to have one example for all three, but not all -that- important. > > > The only example for (3) that I know of is sysvipc sempahores which you also > > mentioned in the paper. Looking through this code, it hasn't changed > > conceptually and it could be a fit for an example (ipc_valid_object() checks > > for whether the object is stale). > > That is indeed the classic canonical example. ;-) > > > 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? Sorry to take you down here..., but what do you mean by "the paper"? ;-/ Thanx, Andrea