From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751569AbdFGJZc (ORCPT ); Wed, 7 Jun 2017 05:25:32 -0400 Received: from mx1.redhat.com ([209.132.183.28]:46936 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751676AbdFGJZa (ORCPT ); Wed, 7 Jun 2017 05:25:30 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 1CF3E80F93 Authentication-Results: ext-mx03.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx03.extmail.prod.ext.phx2.redhat.com; spf=pass smtp.mailfrom=ming.lei@redhat.com DKIM-Filter: OpenDKIM Filter v2.11.0 mx1.redhat.com 1CF3E80F93 Date: Wed, 7 Jun 2017 17:25:12 +0800 From: Ming Lei To: James Wang Cc: axboe@fb.com, hare@suse.com, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, mgorman@suse.com Subject: Re: [PATCH] Fix loop device flush before configure Message-ID: <20170607092511.GB25572@ming.t460p> References: <20170607090104.17337-1-jnwang@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170607090104.17337-1-jnwang@suse.com> User-Agent: Mutt/1.8.0 (2017-02-23) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Wed, 07 Jun 2017 09:25:30 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 07, 2017 at 05:01:04PM +0800, James Wang wrote: > This condition check was exist at before commit b5dd2f6047ca ("block: loop: > improve performance via blk-mq") When add MQ support to loop device, it be > removed because the member of '->lo_thread' be removed. And then upstream > add '->worker_task', I think they forget add it to here. > > When I install SLES-12 product is base on 4.4 kernel, I found installer will > hang +60 second at scan disks. and I found LVM tools would take this action. > finally I found this problem is more obvious on AMD platform. This problem > will impact all scenarios that scan loop devcies. > > When the loop device didn't configure backing file or Request Queue, we > shouldn't to cost a lot of time to flush it. > > Testing steps are following: > modprobe loop max_loop=64 > dd if=/dev/zero of=disk bs=512 count=200K > for((i=0;i<4;i++))do losetup -f disk; done > mkfs.ext4 -F /dev/loop0 > for((i=0;i<4;i++))do mkdir t$i; mount /dev/loop$i t$i;done > for f in `ls /dev/loop[0-9]*|sort`; do \ > echo $f; dd if=$f of=/dev/null bs=512 count=1; \ > done > > Testing data is following: > /dev/loop0 <+patched> > 8.1217e-05 8.3842e-05 > /dev/loop1 > 6.1114e-05 0.000147979 > /dev/loop10 > 0.414701 0.000116564 > /dev/loop11 > 0.7474 6.7942e-05 > /dev/loop12 > 0.747986 8.9082e-05 > /dev/loop13 > 0.746532 7.4799e-05 > /dev/loop14 > 0.480041 9.3926e-05 > /dev/loop15 > 1.26453 7.2522e-05 > > From /dev/loop10 start, loop isn't mounted. but it take more time than > mounted devices. And The data differ by several orders of magnitude. > > Reviewed-by: Hannes Reinecke > > Signed-off-by: James Wang > --- > drivers/block/loop.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/drivers/block/loop.c b/drivers/block/loop.c > index 48f6fa6f810e..c1807e91db08 100644 > --- a/drivers/block/loop.c > +++ b/drivers/block/loop.c > @@ -625,6 +625,9 @@ static int loop_switch(struct loop_device *lo, struct file *file) > */ > static int loop_flush(struct loop_device *lo) > { > + /* loop not yet configured, no running thread, nothing to flush */ > + if (!lo->worker_task) > + return 0; > return loop_switch(lo, NULL); > } Good catch! But looks better to add check like the following if (lo->lo_state != Lo_bound) return 0; because we don't clear lo->worker_task in loop_unprepare_queue() and it is more readable to check on lo->lo_state. thanks, Ming