From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Mon, 2 May 2011 10:48:23 -0400 From: Christoph Hellwig Message-ID: <20110502144823.GA14393@infradead.org> References: <20110428205935.GA24979@redhat.com> <20110429122454.GL32370@agk-dp.fab.redhat.com> <20110502081308.GC8642@agk-dp.fab.redhat.com> <20110502081925.GA11312@infradead.org> <20110502124803.GA31034@redhat.com> <4DBEC3F4.3050804@redhat.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <4DBEC3F4.3050804@redhat.com> Subject: Re: [linux-lvm] do not disable ext4 discards on first discard failure? [was: Re: dm snapshot: ignore discards issued to the snapshot-origin target] Reply-To: LVM general discussion and development List-Id: LVM general discussion and development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , List-Id: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Eric Sandeen Cc: Mike Snitzer , Christoph Hellwig , device-mapper development , DarkNovaNick@gmail.com, linux-lvm@redhat.com, Lukas Czerner , linux-ext4@vger.kernel.org, Alasdair G Kergon On Mon, May 02, 2011 at 09:47:16AM -0500, Eric Sandeen wrote: > I still think we need to stick with the simple rule: "EOPNOTSUPP returned for a particular bio means that it is not supported for that particular bio" - I don't know what else we can do, without creating an ambiguity... > > This does, however, suck for the layer calling in to a complex device. > > What is the overhead for sending discard bios down to a device that does not support it? For a DM-like device there is very little overhead. The bio gets dispatched to make_request and failed in there almost immediately.