From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qa0-f51.google.com (mail-qa0-f51.google.com [209.85.216.51]) by kanga.kvack.org (Postfix) with ESMTP id 750916B0036 for ; Fri, 5 Sep 2014 12:41:17 -0400 (EDT) Received: by mail-qa0-f51.google.com with SMTP id j7so11413656qaq.10 for ; Fri, 05 Sep 2014 09:41:17 -0700 (PDT) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id 74si2242070qgx.64.2014.09.05.09.41.16 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 05 Sep 2014 09:41:16 -0700 (PDT) From: Jeff Moyer Subject: Re: ext4 vs btrfs performance on SSD array References: <20140902000822.GA20473@dastard> <20140902012222.GA21405@infradead.org> <20140903100158.34916d34@notabene.brown> <20140905160808.GA7967@infradead.org> Date: Fri, 05 Sep 2014 12:40:49 -0400 In-Reply-To: <20140905160808.GA7967@infradead.org> (Christoph Hellwig's message of "Fri, 5 Sep 2014 09:08:08 -0700") Message-ID: MIME-Version: 1.0 Content-Type: text/plain Sender: owner-linux-mm@kvack.org List-ID: To: Christoph Hellwig Cc: NeilBrown , Dave Chinner , Nikolai Grigoriev , linux-btrfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-raid@vger.kernel.org, linux-mm@kvack.org, Jens Axboe Christoph Hellwig writes: > On Wed, Sep 03, 2014 at 10:01:58AM +1000, NeilBrown wrote: >> Do we still need maximums at all? > > I don't think we do. At least on any system I work with I have to > increase them to get good performance without any adverse effect on > throttling. > >> So can we just remove the limit on max_sectors and the RAID5 stripe cache >> size? I'm certainly keen to remove the later and just use a mempool if the >> limit isn't needed. >> I have seen reports that a very large raid5 stripe cache size can cause >> a reduction in performance. I don't know why but I suspect it is a bug that >> should be found and fixed. >> >> Do we need max_sectors ?? I'm assuming we're talking about max_sectors_kb in /sys/block/sdX/queue/. > I'll send a patch to remove it and watch for the fireworks.. :) I've seen SSDs that actually degrade in performance if I/O sizes exceed their internal page size (using artificial benchmarks; I never confirmed that with actual workloads). Bumping the default might not be bad, but getting rid of the tunable would be a step backwards, in my opinion. Are you going to bump up BIO_MAX_PAGES while you're at it? Cheers, Jeff -- 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