Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753715AbbGNUqr (ORCPT ); Tue, 14 Jul 2015 16:46:47 -0400 Received: from mx0b-00082601.pphosted.com ([67.231.153.30]:32487 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752269AbbGNUqr (ORCPT ); Tue, 14 Jul 2015 16:46:47 -0400 Message-ID: <55A57507.1030302@fb.com> Date: Tue, 14 Jul 2015 14:45:59 -0600 From: Jens Axboe User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: Mike Snitzer CC: , Subject: Re: [PATCH 3/3] block: by default, limit maximum discard size to 64MB References: <1436899703-31966-1-git-send-email-axboe@fb.com> <1436899703-31966-4-git-send-email-axboe@fb.com> <20150714204419.GA7915@redhat.com> In-Reply-To: <20150714204419.GA7915@redhat.com> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [192.168.54.13] X-Proofpoint-Spam-Reason: safe X-FB-Internal: Safe X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:5.14.151,1.0.33,0.0.0000 definitions=2015-07-14_10:2015-07-14,2015-07-14,1970-01-01 signatures=0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1383 Lines: 35 On 07/14/2015 02:44 PM, Mike Snitzer wrote: > On Tue, Jul 14 2015 at 2:48pm -0400, > Jens Axboe wrote: > >> Lots of devices exhibit very high latencies for big discards, hurting >> reads and writes. By default, limit the max discard we will build to >> 64MB. This value has shown good results across a number of devices. >> >> This will potentially hurt discard throughput, from a provisioning >> point of view (when the user does mkfs.xfs, for instance, and mkfs >> issues a full device discard). If that becomes an issue, we could >> have different behavior for provisioning vs runtime discards. >> >> Signed-off-by: Jens Axboe > > Christoph suggested you impose this default for the specific > drivers/devices that benefit. I'm not following why imposing a 64MB > default is the right thing to do for all devices. I'd argue that's most of them... But the testing we did was on NVMe. I can limit it to NVMe, no big deal. > If this goes in I know for sure I'll need to work around it in DM-thinp. In any case, that's a good point, dm/md should not have their own lower restrictions. -- Jens Axboe -- 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/