From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jens Axboe Subject: Re: [PATCH] block: Add discard flag to blkdev_issue_zeroout() function Date: Wed, 21 Jan 2015 10:42:19 -0700 Message-ID: <54BFE4FB.5090406@kernel.dk> References: <1421802390-7380-1-git-send-email-martin.petersen@oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1421802390-7380-1-git-send-email-martin.petersen@oracle.com> Sender: linux-fsdevel-owner@vger.kernel.org To: "Martin K. Petersen" Cc: linux-scsi@vger.kernel.org, linux-fsdevel@vger.kernel.org List-Id: linux-scsi@vger.kernel.org On 01/20/2015 06:06 PM, Martin K. Petersen wrote: > blkdev_issue_discard() will zero a given block range. This is done by > way of explicit writing, thus provisioning or allocating the blocks on > disk. > > There are use cases where the desired behavior is to zero the blocks but > unprovision them if possible. The blocks must deterministically contain > zeroes when they are subsequently read back. > > This patch adds a flag to blkdev_issue_zeroout() that provides this > variant. If the discard flag is set and a block device guarantees > discard_zeroes_data we will use REQ_DISCARD to clear the block range. If > the device does not support discard_zeroes_data or if the discard > request fails we will fall back to first REQ_WRITE_SAME and then a > regular REQ_WRITE. > > Also update the callers of blkdev_issue_zero() to reflect the new flag > and make sb_issue_zeroout() prefer the discard approach. Applied for 3.20, thanks. -- Jens Axboe