From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ve0-f180.google.com (mail-ve0-f180.google.com [209.85.128.180]) by kanga.kvack.org (Postfix) with ESMTP id 4994E6B0035 for ; Wed, 22 Jan 2014 13:02:17 -0500 (EST) Received: by mail-ve0-f180.google.com with SMTP id db12so442828veb.39 for ; Wed, 22 Jan 2014 10:02:16 -0800 (PST) Received: from mx0a-00082601.pphosted.com (mx0a-00082601.pphosted.com. [67.231.145.42]) by mx.google.com with ESMTP id vq3si4989633veb.103.2014.01.22.10.02.15 for ; Wed, 22 Jan 2014 10:02:15 -0800 (PST) From: Chris Mason Subject: Re: [Lsf-pc] [LSF/MM TOPIC] really large storage sectors - going beyond 4096 bytes Date: Wed, 22 Jan 2014 18:02:09 +0000 Message-ID: <1390413819.1198.20.camel@ret.masoncoding.com> References: <20131220093022.GV11295@suse.de> <52DF353D.6050300@redhat.com> <20140122093435.GS4963@suse.de> <52DFD168.8080001@redhat.com> <20140122143452.GW4963@suse.de> <52DFDCA6.1050204@redhat.com> <20140122151913.GY4963@suse.de> <1390410233.1198.7.camel@ret.masoncoding.com> <1390411300.2372.33.camel@dabdike.int.hansenpartnership.com> In-Reply-To: <1390411300.2372.33.camel@dabdike.int.hansenpartnership.com> Content-Language: en-US Content-Type: text/plain; charset="utf-7" Content-ID: Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Sender: owner-linux-mm@kvack.org List-ID: To: "James.Bottomley@HansenPartnership.com" Cc: "linux-kernel@vger.kernel.org" , "linux-ide@vger.kernel.org" , "lsf-pc@lists.linux-foundation.org" , "linux-mm@kvack.org" , "linux-scsi@vger.kernel.org" , "rwheeler@redhat.com" , "akpm@linux-foundation.org" , "linux-fsdevel@vger.kernel.org" , "mgorman@suse.de" On Wed, 2014-01-22 at 09:21 -0800, James Bottomley wrote: +AD4- On Wed, 2014-01-22 at 17:02 +-0000, Chris Mason wrote: +AFs- I like big sectors and I cannot lie +AF0- +AD4- =20 +AD4- +AD4- I really think that if we want to make progress on this one, we= need +AD4- +AD4- code and someone that owns it. Nick's work was impressive, but= it was +AD4- +AD4- mostly there for getting rid of buffer heads. If we have a dev= ice that +AD4- +AD4- needs it and someone working to enable that device, we'll go fo= rward +AD4- +AD4- much faster. +AD4-=20 +AD4- Do we even need to do that (eliminate buffer heads)? We cope with 4k +AD4- sector only devices just fine today because the bh mechanisms now +AD4- operate on top of the page cache and can do the RMW necessary to upda= te +AD4- a bh in the page cache itself which allows us to do only 4k chunked +AD4- writes, so we could keep the bh system and just alter the granularity= of +AD4- the page cache. +AD4-=20 We're likely to have people mixing 4K drives and +ADw-fill in some other size here+AD4- on the same box. We could just go with the biggest size and use the existing bh code for the sub-pagesized blocks, but I really hesitate to change VM fundamentals for this. >>From a pure code point of view, it may be less work to change it once in the VM. But from an overall system impact point of view, it's a big change in how the system behaves just for filesystem metadata. +AD4- The other question is if the drive does RMW between 4k and whatever i= ts +AD4- physical sector size, do we need to do anything to take advantage of +AD4- it ... as in what would altering the granularity of the page cache bu= y +AD4- us? The real benefit is when and how the reads get scheduled. We're able to do a much better job pipelining the reads, controlling our caches and reducing write latency by having the reads done up in the OS instead of the drive. -chris -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org