Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932303AbdC2LLi (ORCPT ); Wed, 29 Mar 2017 07:11:38 -0400 Received: from mail-vk0-f67.google.com ([209.85.213.67]:34894 "EHLO mail-vk0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755709AbdC2LKI (ORCPT ); Wed, 29 Mar 2017 07:10:08 -0400 MIME-Version: 1.0 In-Reply-To: <20170329105536.GH27994@dhcp22.suse.cz> References: <20170328122559.966310440@linuxfoundation.org> <20170328122601.905696872@linuxfoundation.org> <20170328124312.GE18241@dhcp22.suse.cz> <20170328133040.GJ18241@dhcp22.suse.cz> <20170329104126.GF27994@dhcp22.suse.cz> <20170329105536.GH27994@dhcp22.suse.cz> From: Ilya Dryomov Date: Wed, 29 Mar 2017 13:10:01 +0200 Message-ID: Subject: Re: [PATCH 4.4 48/76] libceph: force GFP_NOIO for socket allocations To: Michal Hocko Cc: Greg Kroah-Hartman , "linux-kernel@vger.kernel.org" , stable@vger.kernel.org, Sergey Jerusalimov , Jeff Layton , linux-xfs@vger.kernel.org Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 941 Lines: 24 On Wed, Mar 29, 2017 at 12:55 PM, Michal Hocko wrote: > On Wed 29-03-17 12:41:26, Michal Hocko wrote: > [...] >> > ceph_con_workfn >> > mutex_lock(&con->mutex) # ceph_connection::mutex >> > try_write >> > ceph_tcp_connect >> > sock_create_kern >> > GFP_KERNEL allocation >> > allocator recurses into XFS, more I/O is issued > > One more note. So what happens if this is a GFP_NOIO request which > cannot make any progress? Your IO thread is blocked on con->mutex > as you write below but the above thread cannot proceed as well. So I am > _really_ not sure this acutally helps. This is not the only I/O worker. A ceph cluster typically consists of at least a few OSDs and can be as large as thousands of OSDs. This is the reason we are calling sock_create_kern() on the writeback path in the first place: pre-opening thousands of sockets isn't feasible. Thanks, Ilya