From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:57760 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750919AbdISOlg (ORCPT ); Tue, 19 Sep 2017 10:41:36 -0400 Date: Tue, 19 Sep 2017 10:41:30 -0400 From: Mike Snitzer To: Ming Lei Cc: "linux-block@vger.kernel.org" , "loberman@redhat.com" , "hch@infradead.org" , "axboe@fb.com" , "dm-devel@redhat.com" , Bart Van Assche Subject: Re: [PATCH 2/5] dm-mpath: return DM_MAPIO_REQUEUE in case of rq allocation failure Message-ID: <20170919144130.GA22469@redhat.com> References: <20170915164456.9803-1-ming.lei@redhat.com> <20170915164456.9803-3-ming.lei@redhat.com> <1505496592.3420.10.camel@wdc.com> <20170915200655.GA28136@redhat.com> <20170917132318.GD6289@ming.t460p> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20170917132318.GD6289@ming.t460p> Sender: linux-block-owner@vger.kernel.org List-Id: linux-block@vger.kernel.org On Sun, Sep 17 2017 at 9:23am -0400, Ming Lei wrote: > On Fri, Sep 15, 2017 at 04:06:55PM -0400, Mike Snitzer wrote: > > On Fri, Sep 15 2017 at 1:29pm -0400, > > Bart Van Assche wrote: > > > > > On Sat, 2017-09-16 at 00:44 +0800, Ming Lei wrote: > > > > blk-mq will rerun queue via RESTART after one request is completion, > > > > so not necessary to wait random time for requeuing, it should trust > > > > blk-mq to do it. > > > > > > > > Signed-off-by: Ming Lei > > > > --- > > > > drivers/md/dm-mpath.c | 2 +- > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > > > diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c > > > > index 96aedaac2c64..f5a1088a6e79 100644 > > > > --- a/drivers/md/dm-mpath.c > > > > +++ b/drivers/md/dm-mpath.c > > > > @@ -505,7 +505,7 @@ static int multipath_clone_and_map(struct dm_target *ti, struct request *rq, > > > > atomic_inc(&m->pg_init_in_progress); > > > > activate_or_offline_path(pgpath); > > > > } > > > > - return DM_MAPIO_DELAY_REQUEUE; > > > > + return DM_MAPIO_REQUEUE; > > > > } > > > > clone->bio = clone->biotail = NULL; > > > > clone->rq_disk = bdev->bd_disk; > > > > > > So you are reverting the patch below? Thank you very much. > > > > > > commit 1c23484c355ec360ca2f37914f8a4802c6baeead > > > Author: Bart Van Assche > > > Date: Wed Aug 9 11:32:12 2017 -0700 > > > > > > dm mpath: do not lock up a CPU with requeuing activity > > > > > > When using the block layer in single queue mode, get_request() > > > returns ERR_PTR(-EAGAIN) if the queue is dying and the REQ_NOWAIT > > > flag has been passed to get_request(). Avoid that the kernel > > > reports soft lockup complaints in this case due to continuous > > > requeuing activity. > > > > > > Fixes: 7083abbbf ("dm mpath: avoid that path removal can trigger an infinite loop") > > > Cc: stable@vger.kernel.org > > > Signed-off-by: Bart Van Assche > > > Tested-by: Laurence Oberman > > > Reviewed-by: Christoph Hellwig > > > Signed-off-by: Mike Snitzer > > > > The problem is that multipath_clone_and_map() is now treated as common > > code (thanks to both blk-mq and old .request_fn now enjoying the use of > > blk_get_request) BUT: Ming please understand that this code is used by > > old .request_fn too. So it would seem that the use of > > Hi Mike, > > OK, thanks for pointing this out. > > > DM_MAPIO_DELAY_REQUEUE vs DM_MAPIO_REQUEUE needs to be based on dm-sq vs > > dm-mq. > > Yeah, just forget that dm-mq can't work on underlying queue which is > block legacy path, also forget the exact reason, :-( Not sure how that detail is relevant to your patch? But here are the 2 patches I posted as RFC to eliminate the restriction: https://patchwork.kernel.org/patch/9839565/ https://patchwork.kernel.org/patch/9839567/ In the end I'm not too interested in supporting blk-mq multipath ontop of block legacy path. But I'd revisit if hch or someone else posted the blk-mq patch that "removed the ->complete handler" (as hch mentions in the thread of the first patchwork patch I reference above). Mike