From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ob0-f178.google.com (mail-ob0-f178.google.com [209.85.214.178]) by kanga.kvack.org (Postfix) with ESMTP id 8FBAD6B0038 for ; Thu, 5 Mar 2015 04:40:25 -0500 (EST) Received: by obbgq1 with SMTP id gq1so12734907obb.2 for ; Thu, 05 Mar 2015 01:40:25 -0800 (PST) Received: from szxga01-in.huawei.com (szxga01-in.huawei.com. [58.251.152.64]) by mx.google.com with ESMTPS id th1si3667392obc.63.2015.03.05.01.39.59 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Thu, 05 Mar 2015 01:40:24 -0800 (PST) Message-ID: <54F8243D.7020809@huawei.com> Date: Thu, 5 Mar 2015 17:39:09 +0800 From: Xishi Qiu MIME-Version: 1.0 Subject: Re: node-hotplug: is memset 0 safe in try_offline_node()? References: <54F52ACF.4030103@huawei.com> <54F81322.8010202@cn.fujitsu.com> In-Reply-To: <54F81322.8010202@cn.fujitsu.com> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Gu Zheng Cc: Yasuaki Ishimatsu , Andrew Morton , Tang Chen , Yinghai Lu , Linux MM , LKML , Toshi Kani , Mel Gorman , Tejun Heo , Kamezawa Hiroyuki On 2015/3/5 16:26, Gu Zheng wrote: > Hi Xishi, > Could you please try the following one? > It postpones the reset of obsolete pgdat from try_offline_node() to > hotadd_new_pgdat(), and just resetting pgdat->nr_zones and > pgdat->classzone_idx to be 0 rather than the whole reset by memset() > as Kame suggested. > > Regards, > Gu > > --- > mm/memory_hotplug.c | 13 ++++--------- > 1 files changed, 4 insertions(+), 9 deletions(-) > > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > index 1778628..c17eebf 100644 > --- a/mm/memory_hotplug.c > +++ b/mm/memory_hotplug.c > @@ -1092,6 +1092,10 @@ static pg_data_t __ref *hotadd_new_pgdat(int nid, u64 start) > return NULL; > > arch_refresh_nodedata(nid, pgdat); > + } else { > + /* Reset the nr_zones and classzone_idx to 0 before reuse */ > + pgdat->nr_zones = 0; > + pgdat->classzone_idx = 0; Hi Gu, This is just to avoid the warning, I think it's no meaning. Here is the changlog from the original patch: commit 88fdf75d1bb51d85ba00c466391770056d44bc03 ... Warn if memory-hotplug/boot code doesn't initialize pg_data_t with zero when it is allocated. Arch code and memory hotplug already initiailize pg_data_t. So this warning should never happen. I select fields *randomly* near the beginning, middle and end of pg_data_t for checking. ... Thanks, Xishi Qiu > } > > /* we can use NODE_DATA(nid) from here */ > @@ -2021,15 +2025,6 @@ void try_offline_node(int nid) > > /* notify that the node is down */ > call_node_notify(NODE_DOWN, (void *)(long)nid); > - > - /* > - * Since there is no way to guarentee the address of pgdat/zone is not > - * on stack of any kernel threads or used by other kernel objects > - * without reference counting or other symchronizing method, do not > - * reset node_data and free pgdat here. Just reset it to 0 and reuse > - * the memory when the node is online again. > - */ > - memset(pgdat, 0, sizeof(*pgdat)); > } > EXPORT_SYMBOL(try_offline_node); > -- 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