From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk0-f198.google.com (mail-qk0-f198.google.com [209.85.220.198]) by kanga.kvack.org (Postfix) with ESMTP id 704EB6B0337 for ; Wed, 7 Feb 2018 11:45:24 -0500 (EST) Received: by mail-qk0-f198.google.com with SMTP id w74so1395926qka.21 for ; Wed, 07 Feb 2018 08:45:24 -0800 (PST) Received: from mx1.redhat.com (mx3-rdu2.redhat.com. [66.187.233.73]) by mx.google.com with ESMTPS id 23si1953563qtr.35.2018.02.07.08.45.23 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 07 Feb 2018 08:45:23 -0800 (PST) Date: Wed, 7 Feb 2018 17:45:13 +0100 From: Jesper Dangaard Brouer Subject: Re: [PATCH 0/2] rcu: Transform kfree_rcu() into kvfree_rcu() Message-ID: <20180207174513.5cc9b503@redhat.com> In-Reply-To: <20180207085700.393f90d0@gandalf.local.home> References: <151791170164.5994.8253310844733420079.stgit@localhost.localdomain> <20180207021703.GC3617@linux.vnet.ibm.com> <20180207042334.GA16175@bombadil.infradead.org> <20180207050200.GH3617@linux.vnet.ibm.com> <20180207083104.GK3617@linux.vnet.ibm.com> <20180207085700.393f90d0@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Steven Rostedt Cc: "Paul E. McKenney" , Kirill Tkhai , Matthew Wilcox , josh@joshtriplett.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, rao.shoaib@oracle.com, brouer@redhat.com On Wed, 7 Feb 2018 08:57:00 -0500 Steven Rostedt wrote: > On Wed, 7 Feb 2018 00:31:04 -0800 > "Paul E. McKenney" wrote: > > > 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. > > Honestly, I don't believe this is an RCU sub-system decision. This is a > memory management decision. > > If we have kmalloc(), vmalloc(), kfree(), vfree() and kvfree(), and we > want kmalloc() to be freed with kfree(), and vmalloc() to be freed with > vfree(), and for strange reasons, we don't know how the data was > allocated we have kvfree(). That's an mm decision not an rcu one. We > should have kfree_rcu(), vfree_rcu() and kvfree_rcu(), and honestly, > they should not depend on kvfree() doing the same thing for everything. > Each should call the corresponding member that they represent. Which > would change this patch set. > > Why? Too much coupling between RCU and MM. What if in the future > something changes and kvfree() goes away or changes drastically. We > would then have to go through all the users of RCU to change them too. > > To me kvfree() is a special case and should not be used by RCU as a > generic function. That would make RCU and MM much more coupled than > necessary. For the record, I fully agree with Steve here. And being a performance "fanatic" I don't like to have the extra branch (and compares) in the free code path... but it's a MM-decision (and sometimes you should not listen to "fanatics" ;-)) void kvfree(const void *addr) { if (is_vmalloc_addr(addr)) vfree(addr); else kfree(addr); } EXPORT_SYMBOL(kvfree); -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer static inline bool is_vmalloc_addr(const void *x) { #ifdef CONFIG_MMU unsigned long addr = (unsigned long)x; return addr >= VMALLOC_START && addr < VMALLOC_END; #else return false; #endif } -- 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