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=-0.9 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, T_DKIMWL_WL_HIGH autolearn=ham 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 37D0AC04ABB for ; Tue, 11 Sep 2018 04:40:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B568C20865 for ; Tue, 11 Sep 2018 04:40:53 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="XrJrX6CP" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B568C20865 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=oracle.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726722AbeIKJiP (ORCPT ); Tue, 11 Sep 2018 05:38:15 -0400 Received: from userp2130.oracle.com ([156.151.31.86]:51532 "EHLO userp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726426AbeIKJiP (ORCPT ); Tue, 11 Sep 2018 05:38:15 -0400 Received: from pps.filterd (userp2130.oracle.com [127.0.0.1]) by userp2130.oracle.com (8.16.0.22/8.16.0.22) with SMTP id w8B4d2HV024986; Tue, 11 Sep 2018 04:40:44 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=subject : to : cc : references : from : message-id : date : mime-version : in-reply-to : content-type : content-transfer-encoding; s=corp-2018-07-02; bh=K6584tUf+jiABk6HMltVlfFhB3coE6drQg86b335fJI=; b=XrJrX6CP21VJhQY7XkKVKJlCmqqtKp7cYy7eSeLkLdryCvQm0x04KKru5k/DKX1j1EBe pK8HVxn6BCO3ineXlIZXQedB6j6rt6wrVgWYkDQcvIeJLOumPjgio9fYMkxep3kkxjh6 t8ktqwqMw5WrpE4dkhaT5v+/BX+qhUwdRiUUcUSjc4BzXny6XXOLO7exShmLxnWZDN21 Fli4+EZ8N0r9QcDP8hdrfgmvjLkqKJFmBsNvJuarH/ykOzL9ARQFzbGaPDElP8fGqJu6 yxGTRF6G+Ka5zznKzQE9g0qNd3RL6aw98kWU1RLYkylzPpAvNHBaH0tougqwiS464RLe zg== Received: from aserv0021.oracle.com (aserv0021.oracle.com [141.146.126.233]) by userp2130.oracle.com with ESMTP id 2mc5ut9kt5-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 11 Sep 2018 04:40:43 +0000 Received: from userv0121.oracle.com (userv0121.oracle.com [156.151.31.72]) by aserv0021.oracle.com (8.14.4/8.14.4) with ESMTP id w8B4ebgL017952 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 11 Sep 2018 04:40:38 GMT Received: from abhmp0002.oracle.com (abhmp0002.oracle.com [141.146.116.8]) by userv0121.oracle.com (8.14.4/8.13.8) with ESMTP id w8B4ebUV015253; Tue, 11 Sep 2018 04:40:37 GMT Received: from [10.182.70.180] (/10.182.70.180) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Mon, 10 Sep 2018 21:40:36 -0700 Subject: Re: [PATCH] percpu-refcount: relax limit on percpu_ref_reinit() To: Ming Lei Cc: linux-kernel@vger.kernel.org, Tejun Heo , Kent Overstreet , linux-block@vger.kernel.org References: <20180909125824.9150-1-ming.lei@redhat.com> <20180910161135.GA27430@ming.t460p> <20180911040323.GC30977@ming.t460p> From: "jianchao.wang" Message-ID: <771fa1eb-85d3-2ff2-6070-207874da85b6@oracle.com> Date: Tue, 11 Sep 2018 12:40:36 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20180911040323.GC30977@ming.t460p> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=9012 signatures=668708 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=488 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1807170000 definitions=main-1809110051 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Ming On 09/11/2018 12:03 PM, Ming Lei wrote: > After the refcount is switched to atomic mode, the whole counting is > done on the atomic part. Then if the refcount need to switch to percpu mode > again, all percpu part of the counter is re-initialized as zero simply. This > is invariant with/without this patch. Does the "whole counting" here means ? (long)(sum (every cpu's refcounter)) + atomic refcounter and when switch to atomic mode, there could be value left in atomic refcounter. then the unsigned long percpu refcounter cound be decreased from 0. >From another angle, one request could be ended on a different cpu from the one where it is issued. Thanks Jianchao