linux-kernel - Re: [PATCH v2 2/2] loop: Better discard support for block devices

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Date:   Wed, 13 Feb 2019 21:39:50 -0500
From:   "Martin K. Petersen" <martin.petersen@...cle.com>
To:     Evan Green <evgreen@...omium.org>
Cc:     Jens Axboe <axboe@...nel.dk>, Bart Van Assche <bvanassche@....org>,
        Gwendal Grignou <gwendal@...omium.org>,
        Martin K Petersen <martin.petersen@...cle.com>,
        Alexis Savery <asavery@...omium.org>,
        Ming Lei <ming.lei@...hat.com>, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] loop: Better discard support for block devices


Evan,

> If the backing device for a loop device is a block device, then mirror
> the discard properties of the underlying block device into the loop
> device. While in there, differentiate between REQ_OP_DISCARD and
> REQ_OP_WRITE_ZEROES, which are different for block devices, but which
> the loop device had just been lumping together.

Bubbling up the queue limits from the backing device is fine. However,
I'm not sure why you are requiring a filesystem to be on a
discard-capable device for REQ_OP_DISCARD to have an effect? Punching a
hole in a file is semantically the same as discarding.

-- 
Martin K. Petersen	Oracle Linux Engineering