From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Snitzer Subject: Re: [PATCH 0/2] Fix blkdev_issue_discard() Date: Wed, 16 Dec 2015 00:12:23 -0500 Message-ID: <20151216051223.GA11688@redhat.com> References: <567034B3.90104@sandisk.com> <20151215154929.GA10785@lst.de> <5670499E.9050501@sandisk.com> Reply-To: device-mapper development Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com To: "Martin K. Petersen" Cc: "linux-block@vger.kernel.org" , Jan Kara , Jens Axboe , dm-devel@redhat.com, Bart Van Assche , Christoph Hellwig List-Id: dm-devel.ids On Tue, Dec 15 2015 at 9:38pm -0500, Martin K. Petersen wrote: > >>>>> "Bart" == Bart Van Assche writes: > > Bart> Should the caller of blkdev_issue_discard() implement this or > Bart> should this functionality be added in blkdev_issue_discard() > Bart> itself ? > > I'm very much against dropping information in the ioctl/filesystem > submission path. But I am not against having a helper function of some > sort that DM and target could use to handle heads and tails. > > Right now DM does not handle this and I think it would be worthwhile to > have. Mike, what are your requirements? If the discard doesn't conform to the device's stacked discard limits then yes the head and/or tail will get dropped on the floor. Not sure why DM is being made the focal point on this. Are you thinking specifically about DM-thinp and its discard_granularity? DM thinp doesn't support partial thinp block discards -- so misaligned/partial discards are dropped by DM thinp. There isn't a compelling case for fixing this (by adding a bitset for each thinp block to support finer grained discards) -- at least not that I'm aware of. But I'm missing exactly what it is your helper function would do... and yet you're asking me what my requirements are.. sorry ;)