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From: Mike Snitzer <snitzer@redhat.com>
To: Pankaj Gupta <pagupta@redhat.com>
Cc: dm-devel@redhat.com, linux-nvdimm@lists.01.org,
	linux-kernel@vger.kernel.org,
	virtualization@lists.linux-foundation.org, kvm@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, linux-acpi@vger.kernel.org,
	qemu-devel@nongnu.org, linux-ext4@vger.kernel.org,
	linux-xfs@vger.kernel.org, dan.j.williams@intel.com,
	zwisler@kernel.org, vishal.l.verma@intel.com,
	dave.jiang@intel.com, mst@redhat.com, jasowang@redhat.com,
	willy@infradead.org, rjw@rjwysocki.net, hch@infradead.org,
	lenb@kernel.org, jack@suse.cz, tytso@mit.edu,
	adilger.kernel@dilger.ca, darrick.wong@oracle.com,
	lcapitulino@redhat.com, kwolf@redhat.com, imammedo@redhat.com,
	jmoyer@redhat.com, nilal@redhat.com, riel@surriel.com,
	stefanha@redhat.com, aarcange@redhat.com, david@redhat.com,
	david@fromorbit.com, cohuck@redhat.com,
	xiaoguangrong.eric@gmail.com, pbonzini@redhat.com,
	yuval.shaia@oracle.com, kilobyte@angband.pl, jstaron@google.com,
	rdunlap@infradead.org
Subject: Re: [PATCH v11 4/7] dm: enable synchronous dax
Date: Mon, 10 Jun 2019 15:28:03 -0400
Message-ID: <20190610192803.GA29002@redhat.com> (raw)
In-Reply-To: <20190610090730.8589-5-pagupta@redhat.com>

On Mon, Jun 10 2019 at  5:07am -0400,
Pankaj Gupta <pagupta@redhat.com> wrote:

>  This patch sets dax device 'DAXDEV_SYNC' flag if all the target
>  devices of device mapper support synchrononous DAX. If device
>  mapper consists of both synchronous and asynchronous dax devices,
>  we don't set 'DAXDEV_SYNC' flag.
> 
> Signed-off-by: Pankaj Gupta <pagupta@redhat.com>
> ---
>  drivers/md/dm-table.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> index 350cf0451456..c5160d846fe6 100644
> --- a/drivers/md/dm-table.c
> +++ b/drivers/md/dm-table.c
> @@ -890,10 +890,17 @@ static int device_supports_dax(struct dm_target *ti, struct dm_dev *dev,
>  			start, len);
>  }
>  
> +static int device_synchronous(struct dm_target *ti, struct dm_dev *dev,
> +				       sector_t start, sector_t len, void *data)
> +{
> +	return dax_synchronous(dev->dax_dev);
> +}
> +
>  bool dm_table_supports_dax(struct dm_table *t, int blocksize)
>  {
>  	struct dm_target *ti;
>  	unsigned i;
> +	bool dax_sync = true;
>  
>  	/* Ensure that all targets support DAX. */
>  	for (i = 0; i < dm_table_get_num_targets(t); i++) {
> @@ -906,7 +913,14 @@ bool dm_table_supports_dax(struct dm_table *t, int blocksize)
>  		    !ti->type->iterate_devices(ti, device_supports_dax,
>  			    &blocksize))
>  			return false;
> +
> +		/* Check devices support synchronous DAX */
> +		if (dax_sync &&
> +		    !ti->type->iterate_devices(ti, device_synchronous, NULL))
> +			dax_sync = false;
>  	}
> +	if (dax_sync)
> +		set_dax_synchronous(t->md->dax_dev);
>  
>  	return true;
>  }
> -- 
> 2.20.1
> 

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?

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

  reply index

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-10  9:07 [PATCH v11 0/7] virtio pmem driver Pankaj Gupta
2019-06-10  9:07 ` [PATCH v11 1/7] libnvdimm: nd_region flush callback support Pankaj Gupta
2019-06-10  9:07 ` [PATCH v11 2/7] virtio-pmem: Add virtio pmem driver Pankaj Gupta
2019-06-10  9:07 ` [PATCH v11 3/7] libnvdimm: add dax_dev sync flag Pankaj Gupta
2019-06-10  9:07 ` [PATCH v11 4/7] dm: enable synchronous dax Pankaj Gupta
2019-06-10 19:28   ` Mike Snitzer [this message]
2019-06-11 13:10     ` [Qemu-devel] " Pankaj Gupta
2019-06-11 15:04       ` Mike Snitzer
2019-06-11 16:04         ` [Qemu-devel] " Pankaj Gupta
2019-06-10  9:07 ` [PATCH v11 5/7] dax: check synchronous mapping is supported Pankaj Gupta
2019-06-10  9:07 ` [PATCH v11 6/7] ext4: disable map_sync for async flush Pankaj Gupta
2019-06-10  9:07 ` [PATCH v11 7/7] xfs: " Pankaj Gupta

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