From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qt0-f197.google.com (mail-qt0-f197.google.com [209.85.216.197]) by kanga.kvack.org (Postfix) with ESMTP id 8C02F6B02E6 for ; Wed, 7 Feb 2018 03:31:02 -0500 (EST) Received: by mail-qt0-f197.google.com with SMTP id z13so35810qth.22 for ; Wed, 07 Feb 2018 00:31:02 -0800 (PST) Received: from mx0a-001b2d01.pphosted.com (mx0a-001b2d01.pphosted.com. [148.163.156.1]) by mx.google.com with ESMTPS id y127si965358qkd.306.2018.02.07.00.31.01 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 07 Feb 2018 00:31:01 -0800 (PST) Received: from pps.filterd (m0098393.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w178UYVe089935 for ; Wed, 7 Feb 2018 03:31:00 -0500 Received: from e11.ny.us.ibm.com (e11.ny.us.ibm.com [129.33.205.201]) by mx0a-001b2d01.pphosted.com with ESMTP id 2fyws9rsgx-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Wed, 07 Feb 2018 03:31:00 -0500 Received: from localhost by e11.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 7 Feb 2018 03:30:58 -0500 Date: Wed, 7 Feb 2018 00:31:04 -0800 From: "Paul E. McKenney" Subject: Re: [PATCH 0/2] rcu: Transform kfree_rcu() into kvfree_rcu() Reply-To: paulmck@linux.vnet.ibm.com References: <151791170164.5994.8253310844733420079.stgit@localhost.localdomain> <20180207021703.GC3617@linux.vnet.ibm.com> <20180207042334.GA16175@bombadil.infradead.org> <20180207050200.GH3617@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Message-Id: <20180207083104.GK3617@linux.vnet.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Kirill Tkhai Cc: Matthew Wilcox , josh@joshtriplett.org, rostedt@goodmis.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, mingo@redhat.com, cl@linux.com, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, brouer@redhat.com, rao.shoaib@oracle.com On Wed, Feb 07, 2018 at 10:57:28AM +0300, Kirill Tkhai wrote: > On 07.02.2018 08:02, Paul E. McKenney wrote: > > On Tue, Feb 06, 2018 at 08:23:34PM -0800, Matthew Wilcox wrote: > >> On Tue, Feb 06, 2018 at 06:17:03PM -0800, Paul E. McKenney wrote: > >>> So it is OK to kvmalloc() something and pass it to either kfree() or > >>> kvfree(), and it had better be OK to kvmalloc() something and pass it > >>> to kvfree(). > >>> > >>> Is it OK to kmalloc() something and pass it to kvfree()? > >> > >> Yes, it absolutely is. > >> > >> void kvfree(const void *addr) > >> { > >> if (is_vmalloc_addr(addr)) > >> vfree(addr); > >> else > >> kfree(addr); > >> } > >> > >>> If so, is it really useful to have two different names here, that is, > >>> both kfree_rcu() and kvfree_rcu()? > >> > >> I think it's handy to have all three of kvfree_rcu(), kfree_rcu() and > >> vfree_rcu() available in the API for the symmetry of calling kmalloc() > >> / kfree_rcu(). > >> > >> Personally, I would like us to rename kvfree() to just free(), and have > >> malloc(x) be an alias to kvmalloc(x, GFP_KERNEL), but I haven't won that > >> fight yet. > > > > But why not just have the existing kfree_rcu() API cover both kmalloc() > > and kvmalloc()? Perhaps I am not in the right forums, but I am not hearing > > anyone arguing that the RCU API has too few members. ;-) > > People, far from RCU internals, consider kfree_rcu() like an extension > of kfree(). And it's not clear it's need to dive into kfree_rcu() comments, > when someone is looking a primitive to free vmalloc'ed memory. Seems like a relatively simple lesson to teach. > Also, construction like > > obj = kvmalloc(); > kfree_rcu(obj); > > makes me think it's legitimately to use plain kfree() as pair bracket to kvmalloc(). So it all works as is, then. > So the significant change of kfree_rcu() behavior will complicate stable backporters > life, because they will need to keep in mind such differences between different > kernel versions. If I understood your construction above, that significant change in kfree_rcu() behavior has already happened. > It seems if we are going to use the single primitive for both kmalloc() > and kvmalloc() memory, it has to have another name. But I don't see problems > with having both kfree_rcu() and kvfree_rcu(). I see problems. We would then have two different names for exactly the same thing. Seems like it would be a lot easier to simply document the existing kfree_rcu() behavior, especially given that it apparently already works. The really doesn't seem to me to be worth a name change. Thanx, Paul -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org