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([2601:647:4d7e:54f3:667:4981:ffa1:7be1]) by smtp.gmail.com with ESMTPSA id y12-20020a62b50c000000b006dab86e675esm211486pfe.185.2024.01.16.17.21.49 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 16 Jan 2024 17:21:50 -0800 (PST) Message-ID: Date: Tue, 16 Jan 2024 17:21:49 -0800 Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [LSF/MM/BPF TOPIC] Improving Zoned Storage Support Content-Language: en-US To: Damien Le Moal , "lsf-pc@lists.linux-foundation.org" Cc: "linux-block@vger.kernel.org" , "linux-scsi@vger.kernel.org" , "linux-nvme@lists.infradead.org" , Christoph Hellwig , Jaegeuk Kim References: <5b3e6a01-1039-4b68-8f02-386f3cc9ddd1@acm.org> From: Bart Van Assche In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 1/16/24 15:34, Damien Le Moal wrote: > On 1/17/24 03:20, Bart Van Assche wrote: >> File system implementers have to decide whether to use Write or Zone >> Append. While the Zone Append command tolerates reordering, with this >> command the filesystem cannot control the order in which the data is >> written on the medium without restricting the queue depth to one. >> Additionally, the latency of write operations is lower compared to zone >> append operations. From [2], a paper with performance results for one >> ZNS SSD model: "we observe that the latency of write operations is lower >> than that of append operations, even if the request size is the same". > > What is the queue depth for this claim ? Hmm ... I haven't found this in the paper. Maybe I overlooked something. >> The mq-deadline I/O scheduler serializes zoned writes even if these got >> reordered by the block layer. However, the mq-deadline I/O scheduler, >> just like any other single-queue I/O scheduler, is a performance >> bottleneck for SSDs that support more than 200 K IOPS. Current NVMe and >> UFS 4.0 block devices support more than 200 K IOPS. > > FYI, I am about to post 20-something patches that completely remove zone write > locking and replace it with "zone write plugging". That is done above the IO > scheduler and also provides zone append emulation for drives that ask for it. > > With this change: > - Zone append emulation is moved to the block layer, as a generic > implementation. sd and dm zone append emulation code is removed. > - Any scheduler can be used, including "none". mq-deadline zone block device > special support is removed. > - Overall, a lot less code (the series removes more code than it adds). > - Reordering problems such as due to IO priority is resolved as well. > > This will need a lot of testing, which we are working on. But your help with > testing on UFS devices will be appreciated as well. That sounds very interesting. I can help with reviewing the kernel patches and also with testing these. Thanks, Bart.