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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 6529CC6778D for ; Tue, 11 Sep 2018 16:05:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2B7DA2086A for ; Tue, 11 Sep 2018 16:05:48 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2B7DA2086A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.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 S1727752AbeIKVFo (ORCPT ); Tue, 11 Sep 2018 17:05:44 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:39166 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727419AbeIKVFn (ORCPT ); Tue, 11 Sep 2018 17:05:43 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 95C0D400C3C1; Tue, 11 Sep 2018 16:05:44 +0000 (UTC) Received: from ming.t460p (ovpn-8-22.pek2.redhat.com [10.72.8.22]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E2C491102E26; Tue, 11 Sep 2018 16:05:38 +0000 (UTC) Date: Wed, 12 Sep 2018 00:05:33 +0800 From: Ming Lei To: Tejun Heo Cc: linux-kernel@vger.kernel.org, Jianchao Wang , Kent Overstreet , linux-block@vger.kernel.org Subject: Re: [PATCH] percpu-refcount: relax limit on percpu_ref_reinit() Message-ID: <20180911160532.GB10082@ming.t460p> References: <20180909125824.9150-1-ming.lei@redhat.com> <20180910164920.GE1100574@devbig004.ftw2.facebook.com> <20180911000049.GB30977@ming.t460p> <20180911134836.GG1100574@devbig004.ftw2.facebook.com> <20180911154540.GA10082@ming.t460p> <20180911154959.GI1100574@devbig004.ftw2.facebook.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180911154959.GI1100574@devbig004.ftw2.facebook.com> User-Agent: Mutt/1.9.1 (2017-09-22) X-Scanned-By: MIMEDefang 2.78 on 10.11.54.3 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.6]); Tue, 11 Sep 2018 16:05:44 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.6]); Tue, 11 Sep 2018 16:05:44 +0000 (UTC) for IP:'10.11.54.3' DOMAIN:'int-mx03.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'ming.lei@redhat.com' RCPT:'' Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 11, 2018 at 08:49:59AM -0700, Tejun Heo wrote: > On Tue, Sep 11, 2018 at 11:45:41PM +0800, Ming Lei wrote: > > > So, this part seems wrong. The function is called percpu_ref_reinit() > > > - the refcnt is expected to be in its initial state with just the base > > > ref once this function returns. If you're removing the restriction on > > > > But the comment says that 'Re-initialize @ref so that it's in the same > > state as when it finished', and this invariant isn't changed with this > > patch. > > The comment goes "when perpcu_ref_init() finished". The function is > called re _init_. It should put the ref in the initial state, right? OK, I am fine to keep the behaviour for this API, will introduce a new helper for NVMe. However, it is doable to switch to percpu mode from atomic mode when it doesn't drop to zero, looks like sort of perpcu_ref_reinit(inherit_old_refcount). Thanks, Ming