From patchwork Wed May 11 21:08:51 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Verma, Vishal L" X-Patchwork-Id: 621278 Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@ozlabs.org Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id 3r4ph84Rc7z9t4P for ; Thu, 12 May 2016 07:11:20 +1000 (AEST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752417AbcEKVKk (ORCPT ); Wed, 11 May 2016 17:10:40 -0400 Received: from mga09.intel.com ([134.134.136.24]:62461 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752505AbcEKVJi (ORCPT ); Wed, 11 May 2016 17:09:38 -0400 Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by orsmga102.jf.intel.com with ESMTP; 11 May 2016 14:09:22 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.24,609,1455004800"; d="scan'208";a="977838239" Received: from omniknight.lm.intel.com ([10.232.112.171]) by fmsmga002.fm.intel.com with ESMTP; 11 May 2016 14:09:22 -0700 From: Vishal Verma To: linux-nvdimm@lists.01.org Cc: Vishal Verma , linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, xfs@oss.sgi.com, linux-ext4@vger.kernel.org, linux-mm@kvack.org, Ross Zwisler , Dan Williams , Dave Chinner , Jan Kara , Jens Axboe , Andrew Morton , linux-kernel@vger.kernel.org, Christoph Hellwig , Jeff Moyer , Boaz Harrosh Subject: [PATCH v7 5/6] dax: for truncate/hole-punch, do zeroing through the driver if possible Date: Wed, 11 May 2016 15:08:51 -0600 Message-Id: <1463000932-31680-6-git-send-email-vishal.l.verma@intel.com> X-Mailer: git-send-email 2.5.5 In-Reply-To: <1463000932-31680-1-git-send-email-vishal.l.verma@intel.com> References: <1463000932-31680-1-git-send-email-vishal.l.verma@intel.com> Sender: linux-ext4-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org In the truncate or hole-punch path in dax, we clear out sub-page ranges. If these sub-page ranges are sector aligned and sized, we can do the zeroing through the driver instead so that error-clearing is handled automatically. For sub-sector ranges, we still have to rely on clear_pmem and have the possibility of tripping over errors. Cc: Dan Williams Cc: Ross Zwisler Cc: Jeff Moyer Cc: Christoph Hellwig Cc: Dave Chinner Cc: Jan Kara Reviewed-by: Christoph Hellwig Signed-off-by: Vishal Verma Reviewed-by: Jan Kara --- Documentation/filesystems/dax.txt | 32 ++++++++++++++++++++++++++++++++ fs/dax.c | 30 +++++++++++++++++++++++++----- 2 files changed, 57 insertions(+), 5 deletions(-) diff --git a/Documentation/filesystems/dax.txt b/Documentation/filesystems/dax.txt index 7bde640..ce4587d 100644 --- a/Documentation/filesystems/dax.txt +++ b/Documentation/filesystems/dax.txt @@ -79,6 +79,38 @@ These filesystems may be used for inspiration: - ext4: the fourth extended filesystem, see Documentation/filesystems/ext4.txt +Handling Media Errors +--------------------- + +The libnvdimm subsystem stores a record of known media error locations for +each pmem block device (in gendisk->badblocks). If we fault at such location, +or one with a latent error not yet discovered, the application can expect +to receive a SIGBUS. Libnvdimm also allows clearing of these errors by simply +writing the affected sectors (through the pmem driver, and if the underlying +NVDIMM supports the clear_poison DSM defined by ACPI). + +Since DAX IO normally doesn't go through the driver/bio path, applications or +sysadmins have an option to restore the lost data from a prior backup/inbuilt +redundancy in the following ways: + +1. Delete the affected file, and restore from a backup (sysadmin route): + This will free the file system blocks that were being used by the file, + and the next time they're allocated, they will be zeroed first, which + happens through the driver, and will clear bad sectors. + +2. Truncate or hole-punch the part of the file that has a bad-block (at least + an entire aligned sector has to be hole-punched, but not necessarily an + entire filesystem block). + +These are the two basic paths that allow DAX filesystems to continue operating +in the presence of media errors. More robust error recovery mechanisms can be +built on top of this in the future, for example, involving redundancy/mirroring +provided at the block layer through DM, or additionally, at the filesystem +level. These would have to rely on the above two tenets, that error clearing +can happen either by sending an IO through the driver, or zeroing (also through +the driver). + + Shortcomings ------------ diff --git a/fs/dax.c b/fs/dax.c index 651d4b1..0b9a169 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -947,6 +947,19 @@ int dax_pfn_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf) } EXPORT_SYMBOL_GPL(dax_pfn_mkwrite); +static bool dax_range_is_aligned(struct block_device *bdev, + unsigned int offset, unsigned int length) +{ + unsigned short sector_size = bdev_logical_block_size(bdev); + + if (!IS_ALIGNED(offset, sector_size)) + return false; + if (!IS_ALIGNED(length, sector_size)) + return false; + + return true; +} + int __dax_zero_page_range(struct block_device *bdev, sector_t sector, unsigned int offset, unsigned int length) { @@ -955,11 +968,18 @@ int __dax_zero_page_range(struct block_device *bdev, sector_t sector, .size = PAGE_SIZE, }; - if (dax_map_atomic(bdev, &dax) < 0) - return PTR_ERR(dax.addr); - clear_pmem(dax.addr + offset, length); - wmb_pmem(); - dax_unmap_atomic(bdev, &dax); + if (dax_range_is_aligned(bdev, offset, length)) { + sector_t start_sector = dax.sector + (offset >> 9); + + return blkdev_issue_zeroout(bdev, start_sector, + length >> 9, GFP_NOFS, true); + } else { + if (dax_map_atomic(bdev, &dax) < 0) + return PTR_ERR(dax.addr); + clear_pmem(dax.addr + offset, length); + wmb_pmem(); + dax_unmap_atomic(bdev, &dax); + } return 0; } EXPORT_SYMBOL_GPL(__dax_zero_page_range);