From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751562AbdECDkX (ORCPT ); Tue, 2 May 2017 23:40:23 -0400 Received: from mail.linux-iscsi.org ([67.23.28.174]:32966 "EHLO linux-iscsi.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751118AbdECDkT (ORCPT ); Tue, 2 May 2017 23:40:19 -0400 Message-ID: <1493782815.23202.85.camel@haakon3.risingtidesystems.com> Subject: Re: [PATCH] tcmu: Recalculate the tcmu_cmd size to save cmd area memories From: "Nicholas A. Bellinger" To: Mike Christie Cc: lixiubo@cmss.chinamobile.com, agrover@redhat.com, namei.unix@gmail.com, sheng@yasker.org, linux-scsi@vger.kernel.org, target-devel@vger.kernel.org, linux-kernel@vger.kernel.org Date: Tue, 02 May 2017 20:40:15 -0700 In-Reply-To: <59093B2B.7000802@redhat.com> References: <1493711669-31508-1-git-send-email-lixiubo@cmss.chinamobile.com> <59093B2B.7000802@redhat.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.4.4-1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2017-05-02 at 21:06 -0500, Mike Christie wrote: > On 05/02/2017 02:54 AM, lixiubo@cmss.chinamobile.com wrote: > > From: Xiubo Li > > > > For the "struct tcmu_cmd_entry" in cmd area, the minimum size > > will be sizeof(struct tcmu_cmd_entry) == 112 Bytes. And it could > > fill about (sizeof(struct rsp) - sizeof(struct req)) / > > sizeof(struct iovec) == 68 / 16 ~= 4 data regions(iov[4]) by > > default. > > > > For most tcmu_cmds, the data block indexes allocated from the > > data area will be continuous. And for the continuous blocks they > > will be merged into the same region using only one iovec. For > > the current code, it will always allocates the same number of > > iovecs with blocks for each tcmu_cmd, and it will wastes much > > memories. > > > > For example, when the block size is 4K and the DATA_OUT buffer > > size is 64K, and the regions needed is less than 5(on my > > environment is almost 99.7%). The current code will allocate > > about 16 iovecs, and there will be (16 - 4) * sizeof(struct > > iovec) = 192 Bytes cmd area memories wasted. > > > > Here adds two helpers to calculate the base size and full size > > of the tcmu_cmd. And will recalculate them again when it make sure > > how many iovs is needed before insert it to cmd area. > > > > Signed-off-by: Xiubo Li > > Looks ok to me. Thanks. > > Acked-by: Mike Christie Applied. Thanks Xiubo + MNC.