From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id BBA26C2BAEE for ; Fri, 13 Mar 2020 03:58:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8F7722072F for ; Fri, 13 Mar 2020 03:58:12 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=joelfernandes.org header.i=@joelfernandes.org header.b="UssdtFo2" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726395AbgCMD6M (ORCPT ); Thu, 12 Mar 2020 23:58:12 -0400 Received: from mail-qk1-f175.google.com ([209.85.222.175]:42965 "EHLO mail-qk1-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726328AbgCMD6M (ORCPT ); Thu, 12 Mar 2020 23:58:12 -0400 Received: by mail-qk1-f175.google.com with SMTP id e11so10329933qkg.9 for ; Thu, 12 Mar 2020 20:58:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=joelfernandes.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=Bh1KG3uVyP7g3HRYxfdszobkMhYkJItQM5mNCYJX6v4=; b=UssdtFo2SLmp4NdTrz4n2ouRMwvj65jU1pbDXpLldKhWNZ0eKYT1tlICIYyK5WxtS6 4zjJsMBsr2Ece0Ip/hAwg0o4Pskd8ERH05D9GsRUo8hhvqbGdjj1NYAQ6K+w7+Bideov zgst17Jqbq9FXpseFD1QF3lKmRjf8RQBzFVII= 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=Bh1KG3uVyP7g3HRYxfdszobkMhYkJItQM5mNCYJX6v4=; b=p/JfAwxhVA62sXFzoLHJ3+7owvgeVjZhQMHHERlsAk5eUNVfiFEYRUBOnmF8ITRwE4 IIlbteTnD6vNNICvypXbN1R2kAgbykUsIO+pGG5ZEugivLi5WWKxzZUlzZqF0XbGjc96 /P/eAYNp4YxHKuOU46O67iMUJnc0Op8I9QEAdp9NLzpjG34Kwuo4GX9HLZkkwDlQsR9Z DpFyjofID1OYkFSvEAkOs4U5PpFm5rhzb+0kIyAObXo+1V88YqJBBEEVzPEzIZgNyb8Y wpMd28aQ+URkr8BrAIbWmdHggiJK/ni043O6Mk74H8XvN/UADDPJeEjc6rkbV4QCV6LN 529g== X-Gm-Message-State: ANhLgQ11KulH2PEUTcj52s5GWWMVloBxGaLaMhVvxwOcbizMp1+Pt3na yFaZDsiNYctZhbkBFS8wHztqaw== X-Google-Smtp-Source: ADFU+vvZpE8trH9aM7UQ1r3PYLFsrlgY5MDyR8aqrnLVhlOThB6v0877UwJTHBx8jkRT87Tl4oPImA== X-Received: by 2002:a37:62d1:: with SMTP id w200mr10895403qkb.399.1584071890645; Thu, 12 Mar 2020 20:58:10 -0700 (PDT) Received: from localhost ([2620:15c:6:12:9c46:e0da:efbf:69cc]) by smtp.gmail.com with ESMTPSA id k66sm16247568qke.10.2020.03.12.20.58.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 12 Mar 2020 20:58:10 -0700 (PDT) Date: Thu, 12 Mar 2020 23:58:09 -0400 From: Joel Fernandes To: Uladzislau Rezki Cc: "Paul E. McKenney" , "joel@joelfernandes.org George Spelvin" , rcu@vger.kernel.org, josh@joshtriplett.org, rostedt@goodmis.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com Subject: Re: Is there a reason we don't have kvfree_rcu()? Message-ID: <20200313035809.GC190951@google.com> References: <20200312162730.GB11889@SDF.ORG> <20200312181138.GI3199@paulmck-ThinkPad-P72> <20200312191009.GA27429@pc636> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200312191009.GA27429@pc636> User-Agent: Mutt/1.12.2 (2019-09-21) Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org On Thu, Mar 12, 2020 at 08:10:09PM +0100, Uladzislau Rezki wrote: > On Thu, Mar 12, 2020 at 11:11:38AM -0700, Paul E. McKenney wrote: > > On Thu, Mar 12, 2020 at 04:27:30PM +0000, George Spelvin wrote: > > > kvfree() is a superset of kfree(), so there's nothing obvious stopping > > > kfree_rcu() from simply changing to kvfree() and everything will keep > > > working. > > > > > > I'd probably add a kvfree_rcu() alias, just for documentation's sake and > > > to make code that depends on the new feature explode at compile time, but > > > it could be identical behind the scenes. > > > > > > There's an existing user in mm/list_lru.c already. > > > > > > I was just thinking of using kvmalloc() in a module, and realized that the > > > lack of a core kvfree_rcu() helper meant I'd have to synchronize_rcu() on > > > module unload. > > > > There was a recent proposal to do just that, but current patches in -rcu > > use kfree_bulk(). It doesn't look to me that this works for kfvree() > > under the covers in its current form. Could it be upgraded to handle > > this case? > > > > Adding Vlad on CC for his thoughts. > > > Paul, see below my view: > > Answering to topic's question it looks like we need kvfree_rcu() support :) > > It is easy to add it actually. But if we are talking about the case when > an object has rcu_head inside. From the other hand recent discussion showed > that we would like to have head-less variant of the kvfree_rcu() functionality: > > https://lkml.org/lkml/2020/2/18/566 > > for example, as Ted pointed, he would go with head-less case(for ext4) only. > The reason is nobody wants to modify internal structures injecting rcu_head > there. Also there are many other places in the kernel where it would be good > to have kfree_rcu() head-less variant as well. > > I spent some time implementing it together with Joel. It is ready from my > side but only for RCU-tree case. Next step is RCU-tiny support, so i am > working on it. > > I can send out an RFC for RCU-tree only support, so we can discuss it > and agree on how to move forward. After that i or Joel or together can > update RCU-tine. > > Joel: What do you think? Yes, your sending an RFC with what you have sounds good. I can prepare a tree for both of us then and we can develop on that. I was actually waiting on your patches so I can add more on top. One more thing I want to add is the shrinker interface to prevent OOM during kfree_rcu() flood. I sent patches to fix that. It works well. We can prepare a tree with all these features and develop on that so there's no conflict. For -tiny and lack of rcu_head, I think we discussed that we would always dynamically allocate rcu_head for that case. > Another thought. We can add kvfree_rcu(ptr, rcu) first, because it is > easy and after that implement head-less case. Yes, that is also fine. We can start simple and then keep improving it. I think we have now 3 users who want head-less interface so ultimately we can shoot for that goal (at later stage). thanks, - Joel