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Date:   Tue, 21 Jan 2020 07:24:59 -0500
From:   Mike Snitzer <snitzer@redhat.com>
To:     Kirill Tkhai <ktkhai@virtuozzo.com>
Cc:     linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        martin.petersen@oracle.com, bob.liu@oracle.com, axboe@kernel.dk,
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Subject: Re: [PATCH v4 6/7] dm: Directly disable max_allocate_sectors for now
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On Tue, Jan 21 2020 at  5:42am -0500,
Kirill Tkhai <ktkhai@virtuozzo.com> wrote:

> Since dm inherits limits from underlining block devices,
> this patch directly disables max_allocate_sectors for dm
> till full allocation support is implemented.
> 
> This prevents high-level primitives (generic_make_request_checks(),
> __blkdev_issue_write_zeroes(), ...) from sending REQ_ALLOCATE
> requests.
> 
> Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
> ---
>  drivers/md/dm-table.c |    2 ++
>  drivers/md/md.h       |    1 +
>  2 files changed, 3 insertions(+)

You're mixing DM and MD changes in the same patch.

But I'm wondering if it might be best to set this default for stacking
devices in blk_set_stacking_limits()?

And then it is up to each stacking driver to override as needed.

Mike