From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-bk0-f48.google.com (mail-bk0-f48.google.com [209.85.214.48]) by kanga.kvack.org (Postfix) with ESMTP id 0ED876B0031 for ; Thu, 23 Jan 2014 16:27:25 -0500 (EST) Received: by mail-bk0-f48.google.com with SMTP id ej10so672351bkb.21 for ; Thu, 23 Jan 2014 13:27:25 -0800 (PST) Received: from ZenIV.linux.org.uk (zeniv.linux.org.uk. [2002:c35c:fd02::1]) by mx.google.com with ESMTPS id ar3si294516bkc.311.2014.01.23.13.27.24 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Thu, 23 Jan 2014 13:27:25 -0800 (PST) Date: Thu, 23 Jan 2014 13:27:14 -0800 From: Joel Becker Subject: Re: [Lsf-pc] [LSF/MM TOPIC] really large storage sectors - going beyond 4096 bytes Message-ID: <20140123212714.GB25376@localhost> References: <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> <1390413819.1198.20.camel@ret.masoncoding.com> <1390414439.2372.53.camel@dabdike.int.hansenpartnership.com> <1390415924.1198.36.camel@ret.masoncoding.com> <1390416421.2372.68.camel@dabdike.int.hansenpartnership.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1390416421.2372.68.camel@dabdike.int.hansenpartnership.com> Sender: owner-linux-mm@kvack.org List-ID: To: James Bottomley Cc: Chris Mason , "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" , "akpm@linux-foundation.org" , "rwheeler@redhat.com" , "linux-fsdevel@vger.kernel.org" , "mgorman@suse.de" On Wed, Jan 22, 2014 at 10:47:01AM -0800, James Bottomley wrote: > On Wed, 2014-01-22 at 18:37 +0000, Chris Mason wrote: > > On Wed, 2014-01-22 at 10:13 -0800, James Bottomley wrote: > > > On Wed, 2014-01-22 at 18:02 +0000, Chris Mason wrote: > [agreement cut because it's boring for the reader] > > > Realistically, if you look at what the I/O schedulers output on a > > > standard (spinning rust) workload, it's mostly large transfers. > > > Obviously these are misalgned at the ends, but we can fix some of that > > > in the scheduler. Particularly if the FS helps us with layout. My > > > instinct tells me that we can fix 99% of this with layout on the FS + io > > > schedulers ... the remaining 1% goes to the drive as needing to do RMW > > > in the device, but the net impact to our throughput shouldn't be that > > > great. > > > > There are a few workloads where the VM and the FS would team up to make > > this fairly miserable > > > > Small files. Delayed allocation fixes a lot of this, but the VM doesn't > > realize that fileA, fileB, fileC, and fileD all need to be written at > > the same time to avoid RMW. Btrfs and MD have setup plugging callbacks > > to accumulate full stripes as much as possible, but it still hurts. > > > > Metadata. These writes are very latency sensitive and we'll gain a lot > > if the FS is explicitly trying to build full sector IOs. > > OK, so these two cases I buy ... the question is can we do something > about them today without increasing the block size? > > The metadata problem, in particular, might be block independent: we > still have a lot of small chunks to write out at fractured locations. > With a large block size, the FS knows it's been bad and can expect the > rolled up newspaper, but it's not clear what it could do about it. > > The small files issue looks like something we should be tackling today > since writing out adjacent files would actually help us get bigger > transfers. ocfs2 can actually take significant advantage here, because we store small file data in-inode. This would grow our in-inode size from ~3K to ~15K or ~63K. We'd actually have to do more work to start putting more than one inode in a block (thought that would be a promising avenue too once the coordination is solved generically. Joel -- "One of the symptoms of an approaching nervous breakdown is the belief that one's work is terribly important." - Bertrand Russell http://www.jlbec.org/ jlbec@evilplan.org -- 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