Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757926AbcCUUCv (ORCPT ); Mon, 21 Mar 2016 16:02:51 -0400 Received: from mail-ig0-f193.google.com ([209.85.213.193]:35211 "EHLO mail-ig0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757643AbcCUUCt (ORCPT ); Mon, 21 Mar 2016 16:02:49 -0400 MIME-Version: 1.0 In-Reply-To: <20160315194244.30093.6483.stgit@birch.djwong.org> References: <20160315194221.30093.70506.stgit@birch.djwong.org> <20160315194244.30093.6483.stgit@birch.djwong.org> From: Mike Snitzer Date: Mon, 21 Mar 2016 14:52:00 -0400 X-Google-Sender-Auth: qEsFsqs9v0A7NJ2vYsTuHRCejEU Message-ID: Subject: Re: [PATCH 3/3] block: implement (some of) fallocate for block devices To: "Darrick J. Wong" Cc: Jens Axboe , Linus Torvalds , Bruce Fields , "Theodore Ts'o" , "Martin K. Petersen" , linux-api@vger.kernel.org, david@fromorbit.com, "linux-kernel@vger.kernel.org" , shane.seymour@hpe.com, Christoph Hellwig , linux-fsdevel , Jeff Layton , Andrew Morton , device-mapper development Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1449 Lines: 29 On Tue, Mar 15, 2016 at 3:42 PM, Darrick J. Wong wrote: > After much discussion, it seems that the fallocate feature flag > FALLOC_FL_ZERO_RANGE maps nicely to SCSI WRITE SAME; and the feature > FALLOC_FL_PUNCH_HOLE maps nicely to the devices that have been > whitelisted for zeroing SCSI UNMAP. Punch still requires that > FALLOC_FL_KEEP_SIZE is set. A length that goes past the end of the > device will be clamped to the device size if KEEP_SIZE is set; or will > return -EINVAL if not. Both start and length must be aligned to the > device's logical block size. > > Since the semantics of fallocate are fairly well established already, > wire up the two pieces. The other fallocate variants (collapse range, > insert range, and allocate blocks) are not supported. I'd like to see fallocate (block allocation) extend down to DM thinp. This more traditional use of fallocate would be useful for ensuring ENOSPC won't occur -- especially important if the FS has committed space in response to fallocate. As of now fallocate doesn't inform DM thinp at all. Curious why you decided not to wire it up? But I'm not sure what "it" (the "allocate blocks" variant) even is given falloc.h doesn't show anything like "_ALLOCATE_BLOCKS"... It would require a new block interface to pass the fallocate extent down. But it seems bizarre to implement "some of" fallocate but not the most widely used case for fallocate. Mike