From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bart Van Assche Subject: Re: [dm-devel] [PATCH v2] staging: writeboost: Add dm-writeboost Date: Fri, 12 Dec 2014 10:12:18 +0100 Message-ID: <548AB172.4000103@acm.org> References: <54883195.1060304@gmail.com> <20141211152626.GA8196@redhat.com> <548A39E7.80508@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <548A39E7.80508@gmail.com> Sender: linux-kernel-owner@vger.kernel.org To: Akira Hayakawa Cc: snitzer@redhat.com, gregkh@linuxfoundation.org, driverdev-devel@linuxdriverproject.org, thornber@redhat.com, linux-kernel@vger.kernel.org, device-mapper development List-Id: dm-devel.ids On 12/12/14 01:42, Akira Hayakawa wrote: > 1. Writeboost shouldn't split the bio into 4KB chunks. > No. It is necessary. > I know WALB (https://github.com/starpos/walb) logs data without > splitting but the data structure becomes complicated. > If you read my code carefully, you will notice that splitting > helps the design simplicity and performance. This is the first time I see someone claiming that reducing the request size improves performance. I don't know any SSD model for which splitting requests improves performance. Additionally, since bio's are split by dm-writeboost, this makes me wonder how atomic writes will ever be supported ? Atomic writes are being standardized by the T10 SCSI committee. I don't think the Linux block layer already supports atomic writes today but I expect support for atomic writes to be added to the block layer sooner or later. See e.g. http://www.t10.org/doc13.htm / SBC-4 SPC-5 Atomic writes and reads for the latest draft specification. Bart.