From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751597AbcFUIwL (ORCPT ); Tue, 21 Jun 2016 04:52:11 -0400 Received: from mail-by2on0074.outbound.protection.outlook.com ([207.46.100.74]:54459 "EHLO na01-by2-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750931AbcFUIwE (ORCPT ); Tue, 21 Jun 2016 04:52:04 -0400 Authentication-Results: spf=pass (sender IP is 63.163.107.21) smtp.mailfrom=sandisk.com; redhat.com; dkim=none (message not signed) header.d=none;redhat.com; dmarc=bestguesspass action=none header.from=sandisk.com; X-AuditID: ac160c69-33fff70000000bcf-8f-5768f648d035 Subject: Re: [RFC] IB/srp: Remove create_workqueue To: Tejun Heo References: <20160607181617.GA6556@Karyakshetra> <20160607192106.GY31708@htj.duckdns.org> <20160620185922.GQ3262@mtj.duckdns.org> CC: Bhaktipriya Shridhar , Doug Ledford , Sean Hefty , Hal Rosenstock , "linux-rdma@vger.kernel.org" , "linux-kernel@vger.kernel.org" From: Bart Van Assche Message-ID: Date: Tue, 21 Jun 2016 10:14:49 +0200 User-Agent: Mozilla/5.0 (X11; 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This work is >>>>> neither queued from inside a shrinker nor by the page writeback code so I >>>>> think it is safe to drop WQ_MEM_RECLAIM. >>>> >>>> It should be able to use system_wq then. >>> >>> No. I have tried that but that resulted in a deadlock. >> >> See also commit bcc059103591 for the details. > > So, create_workqueue() limits concurrency to 1 per cpu and if you have > a dependency between two work items and they get scheduled on the same > cpu they can deadlock. system_wq doesn't have that restriction and > should be fine, AFAICS. Agreed, as long as WQ_DFL_ACTIVE is not reduced from its current value (256) to a very low value (e.g. 1 or 2). This assumption should be documented but I'm not sure what the best way is to document this... Bart.