From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1034289AbdEWVkX (ORCPT ); Tue, 23 May 2017 17:40:23 -0400 Received: from aserp1040.oracle.com ([141.146.126.69]:49704 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1032572AbdEWVkS (ORCPT ); Tue, 23 May 2017 17:40:18 -0400 From: Qing Huang Subject: Re: [PATCH] ib/core: not to set page dirty bit if it's already set. To: Christoph Hellwig References: <20170518233353.14370-1-qing.huang@oracle.com> <20170519130541.GA8017@infradead.org> <9f4a4f90-a7b1-b1dc-6e7a-042f26254681@oracle.com> <20170523074234.GE29525@infradead.org> Cc: linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org, dledford@redhat.com, sean.hefty@intel.com, artemyko@mellanox.com, linux-mm@kvack.org Message-ID: <045c8fb5-fa64-c0e0-c5e4-2734f849a66a@oracle.com> Date: Tue, 23 May 2017 14:39:38 -0700 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: <20170523074234.GE29525@infradead.org> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-Source-IP: userv0021.oracle.com [156.151.31.71] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/23/2017 12:42 AM, Christoph Hellwig wrote: > On Mon, May 22, 2017 at 04:43:57PM -0700, Qing Huang wrote: >> On 5/19/2017 6:05 AM, Christoph Hellwig wrote: >>> On Thu, May 18, 2017 at 04:33:53PM -0700, Qing Huang wrote: >>>> This change will optimize kernel memory deregistration operations. >>>> __ib_umem_release() used to call set_page_dirty_lock() against every >>>> writable page in its memory region. Its purpose is to keep data >>>> synced between CPU and DMA device when swapping happens after mem >>>> deregistration ops. Now we choose not to set page dirty bit if it's >>>> already set by kernel prior to calling __ib_umem_release(). This >>>> reduces memory deregistration time by half or even more when we ran >>>> application simulation test program. >>> As far as I can tell this code doesn't even need set_page_dirty_lock >>> and could just use set_page_dirty >> It seems that set_page_dirty_lock has been used here for more than 10 years. >> Don't know the original purpose. Maybe it was used to prevent races between >> setting dirty bits and swapping out pages? > I suspect copy & paste. Or maybe I don't actually understand the > explanation of set_page_dirty vs set_page_dirty_lock enough. But > I'd rather not hack around the problem. > -- I think there are two parts here. First part is that we don't need to set the dirty bit if it's already set. Second part is whether we use set_page_dirty or set_page_dirty_lock to set dirty bits.