From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jens Axboe Subject: Re: [PATCH] loop: add discard support for loop devices Date: Thu, 18 Aug 2011 21:12:30 +0200 Message-ID: <4E4D641E.5030100@fusionio.com> References: <1313063143-14473-1-git-send-email-lczerner@redhat.com> <4E4D610D.9010701@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Cc: Milan Broz , Jeff Moyer , "linux-kernel@vger.kernel.org" , "achender@linux.vnet.ibm.com" , linux-fsdevel To: Lukas Czerner Return-path: Received: from mx2.fusionio.com ([66.114.96.31]:53084 "EHLO mx2.fusionio.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755087Ab1HRTMi (ORCPT ); Thu, 18 Aug 2011 15:12:38 -0400 In-Reply-To: Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On 2011-08-18 21:08, Lukas Czerner wrote: > On Thu, 18 Aug 2011, Milan Broz wrote: > >> On 08/18/2011 05:49 PM, Lukas Czerner wrote: >>> On Thu, 18 Aug 2011, Jeff Moyer wrote: >>>> Seems you missed the bizarre case of configuring a loop device over top >>>> of a block device. >>> >>> Wow, that is a bizarre case I did not think about at all. But since it >>> is so bizarre, do we even care ? The thing is that the only case where >>> it would make a difference is if the loop device is put on top of block >>> device which actually supports discard. >>> >>> In order to fix that I would need to dig out the actual limits for that >>> device and set that appropriately for the loop device. Is that worth it >>> ? It is not like someone will ever do that (or should) :). >> >> It is bizarre (and being device-mapper developer I surely know better way :-) >> but people are still using that. >> >> Historically one of the use of underlying block device was cryptoloop, but here >> I think it should be completely deprecated (cryptsetup can handle all old loop >> modes as well and default modes for cryptoloop are not safe). >> [Can we finally remove crypto loop option it from kernel? ... ok, just tried:)] >> >> There is also out of tree loop-aes based on heavily patched loop device >> which usually uses block device underneath >> (cryptsetup already can handle all loop-aes modes as well). >> >> Sometimes it is used with --offset parameter for some reason >> (like linear device-mapper mapping). >> >> So I do not care if you do not support discard here but please do not break >> support for block device mapped through loop. > > I do not think that this is the case with my patch. Also, as you know using > discard on encrypted device is not a good idea. It's not a bizarre use case at all, so would be nice to support like we support anything else over a bdev as well. Your patch should not break it, so looks fine. Shall we queue it up for 3.2? It's a good way to beat on fs discard support, fio could be easily configured for that. -- Jens Axboe