linux-ext4 - Re: [PATCH v5 4/5] dm-thin: Add REQ_OP

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Date:   Mon, 1 May 2023 15:15:51 -0400
From:   Mike Snitzer <snitzer@...nel.org>
To:     Sarthak Kukreti <sarthakkukreti@...omium.org>
Cc:     dm-devel@...hat.com, linux-block@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
        Theodore Ts'o <tytso@....edu>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        "Darrick J. Wong" <djwong@...nel.org>,
        Jason Wang <jasowang@...hat.com>,
        Bart Van Assche <bvanassche@...gle.com>,
        Christoph Hellwig <hch@...radead.org>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Daniil Lunev <dlunev@...gle.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Brian Foster <bfoster@...hat.com>,
        Alasdair Kergon <agk@...hat.com>, ejt@...hat.com
Subject: Re: [PATCH v5 4/5] dm-thin: Add REQ_OP_PROVISION support

On Wed, Apr 19 2023 at  8:48P -0400,
Sarthak Kukreti <sarthakkukreti@...omium.org> wrote:

> dm-thinpool uses the provision request to provision
> blocks for a dm-thin device. dm-thinpool currently does not
> pass through REQ_OP_PROVISION to underlying devices.
> 
> For shared blocks, provision requests will break sharing and copy the
> contents of the entire block. Additionally, if 'skip_block_zeroing'
> is not set, dm-thin will opt to zero out the entire range as a part
> of provisioning.
> 
> Signed-off-by: Sarthak Kukreti <sarthakkukreti@...omium.org>
> ---
>  drivers/md/dm-thin.c | 73 +++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 68 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
> index 2b13c949bd72..58d633f5c928 100644
> --- a/drivers/md/dm-thin.c
> +++ b/drivers/md/dm-thin.c
> @@ -1891,7 +1893,8 @@ static void process_shared_bio(struct thin_c *tc, struct bio *bio,
>  
>  	if (bio_data_dir(bio) == WRITE && bio->bi_iter.bi_size) {
>  		break_sharing(tc, bio, block, &key, lookup_result, data_cell);
> -		cell_defer_no_holder(tc, virt_cell);
> +		if (bio_op(bio) != REQ_OP_PROVISION)
> +			cell_defer_no_holder(tc, virt_cell);

Can you please explain why cell_defer_no_holder() is skipped for REQ_OP_PROVISION here?

Thanks,
Mike