Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934361AbaLLJM0 (ORCPT ); Fri, 12 Dec 2014 04:12:26 -0500 Received: from baptiste.telenet-ops.be ([195.130.132.51]:35506 "EHLO baptiste.telenet-ops.be" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758878AbaLLJMV (ORCPT ); Fri, 12 Dec 2014 04:12:21 -0500 Message-ID: <548AB172.4000103@acm.org> Date: Fri, 12 Dec 2014 10:12:18 +0100 From: Bart Van Assche User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0 MIME-Version: 1.0 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 Subject: Re: [dm-devel] [PATCH v2] staging: writeboost: Add dm-writeboost References: <54883195.1060304@gmail.com> <20141211152626.GA8196@redhat.com> <548A39E7.80508@gmail.com> In-Reply-To: <548A39E7.80508@gmail.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/