linux-kernel - Re: [PATCH v4 6/7] dm: Directly disable max_allocate

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Date:   Tue, 21 Jan 2020 07:24:59 -0500
From:   Mike Snitzer <snitzer@...hat.com>
To:     Kirill Tkhai <ktkhai@...tuozzo.com>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        martin.petersen@...cle.com, bob.liu@...cle.com, axboe@...nel.dk,
        agk@...hat.com, dm-devel@...hat.com, song@...nel.org,
        tytso@....edu, adilger.kernel@...ger.ca,
        Chaitanya.Kulkarni@....com, darrick.wong@...cle.com,
        ming.lei@...hat.com, osandov@...com, jthumshirn@...e.de,
        minwoo.im.dev@...il.com, damien.lemoal@....com,
        andrea.parri@...rulasolutions.com, hare@...e.com, tj@...nel.org,
        ajay.joshi@....com, sagi@...mberg.me, dsterba@...e.com,
        bvanassche@....org, dhowells@...hat.com, asml.silence@...il.com
Subject: Re: [PATCH v4 6/7] dm: Directly disable max_allocate_sectors for now

On Tue, Jan 21 2020 at  5:42am -0500,
Kirill Tkhai <ktkhai@...tuozzo.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@...tuozzo.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