From: "Martin K. Petersen" Subject: Re: [RFC] fadvise: add more flags to provide a hint for block allocation Date: Wed, 07 Mar 2012 23:23:49 -0500 Message-ID: References: <20120305125029.GA5121@gmail.com> <20120307005130.GH3592@dastard> <20120307121138.GK3592@dastard> Mime-Version: 1.0 Content-Type: text/plain Cc: "Martin K. Petersen" , Andreas Dilger , linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org To: Dave Chinner Return-path: Received: from acsinet15.oracle.com ([141.146.126.227]:43916 "EHLO acsinet15.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752393Ab2CHEX6 (ORCPT ); Wed, 7 Mar 2012 23:23:58 -0500 In-Reply-To: <20120307121138.GK3592@dastard> (Dave Chinner's message of "Wed, 7 Mar 2012 23:11:38 +1100") Sender: linux-ext4-owner@vger.kernel.org List-ID: >>>>> "Dave" == Dave Chinner writes: Dave> From what I've seen of the proposed SMR device standards, we're Dave> going to have to redesign filesystem allocation policies [...] The initial proposal involved SMR disks having a sparse LBA map carved into 2GB chunks. However, that was shot down pretty hard. The approach currently being worked uses either dynamic (flash, tiered storage) or static hints (SMR) to put things in an appropriate area given the nature of the I/O. This puts the burden of virtual to physical LBA management on the device rather than in the filesystem allocators. And gives us the benefit of having a single interface that can be used for many different device types. That said, the current proposal is crazy complex and clearly written with Windows in mind. They are creating different access profiles for .DLLs, .INI files, apps in the startup folder, and so on. Dave> Indeed, there is no end of different allocation policies a Dave> filesystem could define, so I don't think that iterating them in Dave> fadvise() is a good thing to do. I have no particular opinion on the proposed fadvise() flags. Just saying that no matter whether we like it or not we'll have to be able to pass information about expected access patterns down to the storage. -- Martin K. Petersen Oracle Linux Engineering