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 1FFAF6B0038 for ; Thu, 21 Dec 2017 20:39:29 -0500 (EST) Received: by mail-qk0-f198.google.com with SMTP id c142so16043359qke.15 for ; Thu, 21 Dec 2017 17:39:29 -0800 (PST) Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com. [148.163.158.5]) by mx.google.com with ESMTPS id r32si1395800qtr.253.2017.12.21.17.39.28 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 21 Dec 2017 17:39:28 -0800 (PST) Received: from pps.filterd (m0098417.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.21/8.16.0.21) with SMTP id vBM1ZipT066453 for ; Thu, 21 Dec 2017 20:39:28 -0500 Received: from e13.ny.us.ibm.com (e13.ny.us.ibm.com [129.33.205.203]) by mx0a-001b2d01.pphosted.com with ESMTP id 2f0kqy3pxj-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Thu, 21 Dec 2017 20:39:27 -0500 Received: from localhost by e13.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 21 Dec 2017 20:39:27 -0500 Date: Thu, 21 Dec 2017 17:39:37 -0800 From: "Paul E. McKenney" Subject: Re: [PATCH] Move kfree_call_rcu() to slab_common.c Reply-To: paulmck@linux.vnet.ibm.com References: <1513844387-2668-1-git-send-email-rao.shoaib@oracle.com> <20171221123630.GB22405@bombadil.infradead.org> <44044955-1ef9-1d1e-5311-d8edc006b812@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <44044955-1ef9-1d1e-5311-d8edc006b812@oracle.com> Message-Id: <20171222013937.GA7829@linux.vnet.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Rao Shoaib Cc: Matthew Wilcox , linux-kernel@vger.kernel.org, brouer@redhat.com, linux-mm@kvack.org On Thu, Dec 21, 2017 at 09:31:23AM -0800, Rao Shoaib wrote: > > > On 12/21/2017 04:36 AM, Matthew Wilcox wrote: > >On Thu, Dec 21, 2017 at 12:19:47AM -0800, rao.shoaib@oracle.com wrote: > >>This patch moves kfree_call_rcu() and related macros out of rcu code. A new > >>function __call_rcu_lazy() is created for calling __call_rcu() with the lazy > >>flag. > >Something you probably didn't know ... there are two RCU implementations > >in the kernel; Tree and Tiny. It looks like you've only added > >__call_rcu_lazy() to Tree and you'll also need to add it to Tiny. > I left it out on purpose because the call in tiny is a little different > > rcutiny.h: > > static inline void kfree_call_rcu(struct rcu_head *head, > void (*func)(struct rcu_head *rcu)) > { > call_rcu(head, func); > } > > tree.c: > > void kfree_call_rcu(struct rcu_head *head, > void (*func)(struct rcu_head *rcu)) > { > __call_rcu(head, func, rcu_state_p, -1, 1); > } > EXPORT_SYMBOL_GPL(kfree_call_rcu); > > If we want the code to be exactly same I can create a lazy version > for tiny as well. However, I don not know where to move > kfree_call_rcu() from it's current home in rcutiny.h though. Any > thoughts ? I might be missing something subtle here, but in case I am not, my suggestion is to simply rename rcutiny.h's kfree_call_rcu() and otherwise leave it as is. If you want to update the type of the second argument, which got missed back in the day, there is always this: static inline void call_rcu_lazy(struct rcu_head *head, rcu_callback_t func) { call_rcu(head, func); } The reason that Tiny RCU doesn't handle laziness specially is because Tree RCU's handling of laziness is a big no-op on the single CPU systems on which Tiny RCU runs. So Tiny RCU need do nothing special to support laziness. Thanx, Paul > >>Also moving macros generated following checkpatch noise. I do not know > >>how to silence checkpatch as there is nothing wrong. > >> > >>CHECK: Macro argument reuse 'offset' - possible side-effects? > >>#91: FILE: include/linux/slab.h:348: > >>+#define __kfree_rcu(head, offset) \ > >>+ do { \ > >>+ BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); \ > >>+ kfree_call_rcu(head, (rcu_callback_t)(unsigned long)(offset)); \ > >>+ } while (0) > >What checkpatch is warning you about here is that somebody might call > > > >__kfree_rcu(p, a++); > > > >and this would expand into > > > > do { \ > > BUILD_BUG_ON(!__is_kfree_rcu_offset(a++)); \ > > kfree_call_rcu(p, (rcu_callback_t)(unsigned long)(a++)); \ > > } while (0) > > > >which would increment 'a' twice, and cause pain and suffering. > > > >That's pretty unlikely usage of __kfree_rcu(), but I suppose it's not > >impossible. We have various hacks to get around this kind of thing; > >for example I might do this as:: > > > >#define __kfree_rcu(head, offset) \ > > do { \ > > unsigned long __o = offset; > > BUILD_BUG_ON(!__is_kfree_rcu_offset(__o)); \ > > kfree_call_rcu(head, (rcu_callback_t)(unsigned long)(__o)); \ > > } while (0) > > > >Now offset is only evaluated once per invocation of the macro. The other > >two warnings are the same problem. > > > Thanks. I was not sure if I was required to fix the noise or based > on inspection the noise could be ignored. I will make the change and > resubmit. > > Shoaib > -- 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