Subject: Re: [Drbd-dev] [PATCH 11/30] drbd: when receiving P_TRIM, zero-out
 partial unaligned chunks
To: Philipp Reisner <philipp.reisner@linbit.com>, Jens Axboe <axboe@fb.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
References: <1461586077-11581-1-git-send-email-philipp.reisner@linbit.com>
 <1461586077-11581-12-git-send-email-philipp.reisner@linbit.com>
CC: Lars Ellenberg <lars.ellenberg@linbit.com>,
        "drbd-dev@lists.linbit.com" <drbd-dev@lists.linbit.com>
From: Bart Van Assche <bart.vanassche@sandisk.com>
Message-ID: <571E47C8.5010805@sandisk.com>
Date: Mon, 25 Apr 2016 09:37:28 -0700
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On 04/25/2016 05:13 AM, Philipp Reisner wrote:
> +	while (nr_sectors >= granularity) {
> +		nr = min_t(sector_t, nr_sectors, max_discard_sectors);
> +		err |= blkdev_issue_discard(bdev, start, nr, GFP_NOIO, 0);
> +		nr_sectors -= nr;
> +		start += nr;
> +	}

Hello Phil,

In blk_bio_discard_split() the following statement protects against 
block drivers for which max_discard_sectors is not a multiple of the 
discard granularity:

	max_discard_sectors -= max_discard_sectors % granularity;

Do we need something similar in the above loop?

To Jens: should the drbd_issue_discard_or_zero_out() function go 
upstream or should rather what this function does be integrated in 
blkdev_issue_zeroout() as is done by the patch series "[PATCH v2 0/6] 
Make blkdev_issue_discard() submit aligned discard requests" 
(http://thread.gmane.org/gmane.linux.kernel.device-mapper.devel/23801)?

Thanks,

Bart.