From: Vishal Verma Subject: [PATCH v5 4/5] dax: for truncate/hole-punch, do zeroing through the driver if possible Date: Fri, 6 May 2016 15:53:10 -0600 Message-ID: <1462571591-3361-5-git-send-email-vishal.l.verma@intel.com> References: <1462571591-3361-1-git-send-email-vishal.l.verma@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Jens Axboe , Jan Kara , Andrew Morton , Christoph Hellwig , Vishal Verma , linux-kernel@vger.kernel.org, xfs@oss.sgi.com, linux-block@vger.kernel.org, linux-mm@kvack.org, Jeff Moyer , Boaz Harrosh , linux-fsdevel@vger.kernel.org, Ross Zwisler , linux-ext4@vger.kernel.org, Dan Williams To: linux-nvdimm@lists.01.org Return-path: In-Reply-To: <1462571591-3361-1-git-send-email-vishal.l.verma@intel.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: xfs-bounces@oss.sgi.com Sender: xfs-bounces@oss.sgi.com List-Id: 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 Signed-off-by: Vishal Verma --- 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 5948d9b..d8c974e 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -1196,6 +1196,20 @@ out: } EXPORT_SYMBOL_GPL(dax_pfn_mkwrite); +static bool dax_range_is_aligned(struct block_device *bdev, + struct blk_dax_ctl *dax, unsigned int offset, + unsigned int length) +{ + unsigned short sector_size = bdev_logical_block_size(bdev); + + if (((u64)dax->addr + offset) % sector_size) + return false; + if (length % sector_size) + return false; + + return true; +} + /** * dax_zero_page_range - zero a range within a page of a DAX file * @inode: The file being truncated @@ -1240,11 +1254,17 @@ int dax_zero_page_range(struct inode *inode, loff_t from, unsigned length, .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, &dax, offset, length)) + return blkdev_issue_zeroout(bdev, dax.sector, + length / bdev_logical_block_size(bdev), + 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; -- 2.5.5 _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs