From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Christie Subject: Re: [PATCH] tcmu: Recalculate the tcmu_cmd size to save cmd area memories Date: Tue, 2 May 2017 21:06:35 -0500 Message-ID: <59093B2B.7000802@redhat.com> References: <1493711669-31508-1-git-send-email-lixiubo@cmss.chinamobile.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1493711669-31508-1-git-send-email-lixiubo@cmss.chinamobile.com> Sender: target-devel-owner@vger.kernel.org To: lixiubo@cmss.chinamobile.com, nab@linux-iscsi.org Cc: 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 List-Id: linux-scsi@vger.kernel.org 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