On Tue, Sep 19, 2017 at 10:41:30AM -0400, Mike Snitzer wrote:
> On Sun, Sep 17 2017 at 9:23am -0400,
> Ming Lei <ming.lei@xxxxxxxxxx> 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 <Bart.VanAssche@xxxxxxx> 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 <ming.lei@xxxxxxxxxx>
> > > > > ---
> > > > > 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 <bart.vanassche@xxxxxxx>
> > > > 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@xxxxxxxxxxxxxxx
> > > > Signed-off-by: Bart Van Assche <bart.vanassche@xxxxxxx>
> > > > Tested-by: Laurence Oberman <loberman@xxxxxxxxxx>
> > > > Reviewed-by: Christoph Hellwig <hch@xxxxxx>
> > > > Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
> > >
> > > 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/
Thanks for the posting.
>
> 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).
If blk-mq mpath can be ontop of both block legacy and blk-mq,
the legacy .request_fn can be removed from dm mpath, that can
be a big simplification, especially the global parameter of
use_blk_mq may exist for a bit long.
--
Ming
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