linux-kernel - Re: [PATCH v9 4/7] dm: enable synchronous dax

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Date:   Wed, 15 May 2019 13:48:57 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Mike Snitzer <snitzer@...hat.com>
Cc:     linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        virtualization@...ts.linux-foundation.org,
        KVM list <kvm@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux ACPI <linux-acpi@...r.kernel.org>,
        Qemu Developers <qemu-devel@...gnu.org>,
        linux-ext4 <linux-ext4@...r.kernel.org>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        Ross Zwisler <zwisler@...nel.org>,
        Vishal L Verma <vishal.l.verma@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Christoph Hellwig <hch@...radead.org>,
        Len Brown <lenb@...nel.org>, Jan Kara <jack@...e.cz>,
        "Theodore Ts'o" <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        lcapitulino@...hat.com, Kevin Wolf <kwolf@...hat.com>,
        Igor Mammedov <imammedo@...hat.com>,
        jmoyer <jmoyer@...hat.com>,
        Nitesh Narayan Lal <nilal@...hat.com>,
        Rik van Riel <riel@...riel.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        david <david@...morbit.com>, cohuck@...hat.com,
        Xiao Guangrong <xiaoguangrong.eric@...il.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Adam Borowski <kilobyte@...band.pl>,
        yuval shaia <yuval.shaia@...cle.com>, jstaron@...gle.com,
        Pankaj Gupta <pagupta@...hat.com>,
        device-mapper development <dm-devel@...hat.com>
Subject: Re: [PATCH v9 4/7] dm: enable synchronous dax

[ add Mike and dm-devel ]

Mike, any concerns with the below addition to the device-mapper-dax
implementation?

On Tue, May 14, 2019 at 7:58 AM Pankaj Gupta <pagupta@...hat.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@...hat.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 cde3b49b2a91..1cce626ff576 100644
> --- a/drivers/md/dm-table.c
> +++ b/drivers/md/dm-table.c
> @@ -886,10 +886,17 @@ static int device_supports_dax(struct dm_target *ti, struct dm_dev *dev,
>         return bdev_dax_supported(dev->bdev, PAGE_SIZE);
>  }
>
> +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);
> +}
> +
>  static bool dm_table_supports_dax(struct dm_table *t)
>  {
>         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++) {
> @@ -901,7 +908,14 @@ static bool dm_table_supports_dax(struct dm_table *t)
>                 if (!ti->type->iterate_devices ||
>                     !ti->type->iterate_devices(ti, device_supports_dax, NULL))
>                         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
>