linux-ext4 - Re: [Qemu-devel] [PATCH v11 4/7] dm: enable synchronous dax

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Date:   Tue, 11 Jun 2019 12:04:21 -0400 (EDT)
From:   Pankaj Gupta <pagupta@...hat.com>
To:     Mike Snitzer <snitzer@...hat.com>
Cc:     rdunlap@...radead.org, jack@...e.cz, kvm@...r.kernel.org,
        mst@...hat.com, jasowang@...hat.com, david@...morbit.com,
        qemu-devel@...gnu.org, virtualization@...ts.linux-foundation.org,
        dm-devel@...hat.com, adilger kernel <adilger.kernel@...ger.ca>,
        zwisler@...nel.org, aarcange@...hat.com,
        dave jiang <dave.jiang@...el.com>, jstaron@...gle.com,
        linux-nvdimm@...ts.01.org,
        vishal l verma <vishal.l.verma@...el.com>, david@...hat.com,
        willy@...radead.org, hch@...radead.org, linux-acpi@...r.kernel.org,
        jmoyer@...hat.com, linux-ext4@...r.kernel.org, lenb@...nel.org,
        kilobyte@...band.pl, riel@...riel.com,
        yuval shaia <yuval.shaia@...cle.com>, stefanha@...hat.com,
        imammedo@...hat.com, dan j williams <dan.j.williams@...el.com>,
        lcapitulino@...hat.com, kwolf@...hat.com, nilal@...hat.com,
        tytso@....edu, xiaoguangrong eric <xiaoguangrong.eric@...il.com>,
        cohuck@...hat.com, rjw@...ysocki.net, linux-kernel@...r.kernel.org,
        linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        pbonzini@...hat.com, darrick wong <darrick.wong@...cle.com>
Subject: Re: [Qemu-devel] [PATCH v11 4/7] dm: enable synchronous dax



> 
> > Hi Mike,
> > 
> > Thanks for the review Please find my reply inline.
> > 
> > > 
> > > dm_table_supports_dax() is called multiple times (from
> > > dm_table_set_restrictions and dm_table_determine_type).  It is strange
> > > to have a getter have a side-effect of being a setter too.  Overloading
> > > like this could get you in trouble in the future.
> > > 
> > > Are you certain this is what you want?
> > 
> > I agree with you.
> > 
> > > 
> > > Or would it be better to refactor dm_table_supports_dax() to take an
> > > iterate_devices_fn arg and have callers pass the appropriate function?
> > > Then have dm_table_set_restrictions() caller do:
> > > 
> > >      if (dm_table_supports_dax(t, device_synchronous, NULL))
> > >                set_dax_synchronous(t->md->dax_dev);
> > > 
> > > (NULL arg implies dm_table_supports_dax() refactoring would take a int
> > > *data pointer rather than int type).
> > > 
> > > Mike
> > > 
> > 
> > I am sending below patch as per your suggestion. Does it look
> > near to what you have in mind?
> 
> Yes, it does.. just one nit I noticed inlined below.
> 
> > diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> > index 350cf0451456..8d89acc8b8c2 100644
> > --- a/drivers/md/dm-table.c
> > +++ b/drivers/md/dm-table.c
> 
> ...
> 
> > @@ -1910,8 +1919,13 @@ void dm_table_set_restrictions(struct dm_table *t,
> > struct request_queue *q,
> >         }
> >         blk_queue_write_cache(q, wc, fua);
> > 
> > -       if (dm_table_supports_dax(t, PAGE_SIZE))
> > +       if (dm_table_supports_dax(t, device_supports_dax, &page_size)) {
> > +
> 
> No need for an empty newline here ^

Sure. Will remove this and send official v12 patchset with the updated patch 4.

Thanks,
Pankaj

> 
> >                 blk_queue_flag_set(QUEUE_FLAG_DAX, q);
> > +               if (dm_table_supports_dax(t, device_synchronous, NULL))
> > +                       set_dax_synchronous(t->md->dax_dev);
> > +       }
> >         else
> >                 blk_queue_flag_clear(QUEUE_FLAG_DAX, q);
> > 
> 
> Thanks,
> Mike
> 
>