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([240b:10:2720:5510:a182:288:3ffa:432a]) by smtp.gmail.com with ESMTPSA id m11sm2739481pjl.18.2020.03.24.09.51.25 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 24 Mar 2020 09:51:26 -0700 (PDT) Subject: Re: [PATCH] block, nvme: Increase max segments parameter setting value To: Keith Busch Cc: Chaitanya Kulkarni , "linux-block@vger.kernel.org" , "linux-nvme@lists.infradead.org" References: <20200323182324.3243-1-ikegami.t@gmail.com> <20200324000237.GB15091@redsun51.ssa.fujisawa.hgst.com> From: Tokunori Ikegami Message-ID: <6b73db44-ca3f-4285-0c91-dc1b1a5ca9f1@gmail.com> Date: Wed, 25 Mar 2020 01:51:23 +0900 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20200324000237.GB15091@redsun51.ssa.fujisawa.hgst.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 2020/03/24 9:02, Keith Busch wrote: > On Tue, Mar 24, 2020 at 08:09:19AM +0900, Tokunori Ikegami wrote: >> Hi, >>> The change looks okay, but why do we need such a large data length ? >>> >>> Do you have a use-case or performance numbers ? >> We use the large data length to get log page by the NVMe admin command. >> In the past it was able to get with the same length but failed currently >> with it. >> >> So it seems that depended on the kernel version as caused by the version up. > We didn't have 32-bit max segments before, though. Why was 16-bits > enough in older kernels? Which kernel did this stop working? Now I am asking the detail information to the reporter so let me update later. That was able to use the same command script with the large data length in the past. > >> Also I have confirmed that currently failed with the length 0x10000000 >> 256MB. > If your hitting max segment limits before any other limit, you should be > able to do larger transfers with more physically contiguous memory. Huge > pages can get the same data length in fewer segments, if you want to > try that. > > But wouldn't it be better if your application splits the transfer into > smaller chunks across multiple commands? NVMe log page command supports > offsets for this reason. Yes actually now we are using the offset parameter to split the data to get. For a future usage it seems that it is better to use the large number size also.