| Message ID | 1462906156-22303-5-git-send-email-vishal.l.verma@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hi Vishal, can you also pick up the my patch to add a low-level __dax_zero_range that I cced you on? That way we can avoid a nasty merge conflict with my xfs/iomap changes. -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Tue, 2016-05-10 at 12:25 -0700, Christoph Hellwig wrote: > Hi Vishal, > > can you also pick up the my patch to add a low-level __dax_zero_range > that I cced you on? That way we can avoid a nasty merge conflict with > my xfs/iomap changes. Good idea - I'll do that for the next posting. I'll wait a day or two for any additional reviews/acks. I'm looking to get all this into a branch in the nvdimm tree once Jan splits up his dax-locking series.. Mostly I guess I'm looking for a yay or nay for the block layer changes (patch 2). Jens?
On Tue 10-05-16 12:49:15, Vishal Verma wrote: > 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 <dan.j.williams@intel.com> > Cc: Ross Zwisler <ross.zwisler@linux.intel.com> > Cc: Jeff Moyer <jmoyer@redhat.com> > Cc: Christoph Hellwig <hch@infradead.org> > Cc: Dave Chinner <david@fromorbit.com> > Cc: Jan Kara <jack@suse.cz> > Reviewed-by: Christoph Hellwig <hch@lst.de> > Signed-off-by: Vishal Verma <vishal.l.verma@intel.com> ... > +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 (!IS_ALIGNED(((u64)dax->addr + offset), sector_size)) One more question: 'dax' is initialized in dax_zero_page_range() and dax->addr is going to be always NULL here. So either you forgot to call dax_map_atomic() to get the addr or the use of dax->addr is just bogus (which is what I currently believe since I see no way how the address could be unaligned with the sector_size)... Honza > + return false; > + if (!IS_ALIGNED(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 +1254,16 @@ 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 >> 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; > -- > 2.5.5 >
On Wed, 2016-05-11 at 10:15 +0200, Jan Kara wrote: > On Tue 10-05-16 12:49:15, Vishal Verma wrote: > > > > 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 <dan.j.williams@intel.com> > > Cc: Ross Zwisler <ross.zwisler@linux.intel.com> > > Cc: Jeff Moyer <jmoyer@redhat.com> > > Cc: Christoph Hellwig <hch@infradead.org> > > Cc: Dave Chinner <david@fromorbit.com> > > Cc: Jan Kara <jack@suse.cz> > > Reviewed-by: Christoph Hellwig <hch@lst.de> > > Signed-off-by: Vishal Verma <vishal.l.verma@intel.com> > ... > > > > > +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 (!IS_ALIGNED(((u64)dax->addr + offset), sector_size)) > One more question: 'dax' is initialized in dax_zero_page_range() and > dax->addr is going to be always NULL here. So either you forgot to > call > dax_map_atomic() to get the addr or the use of dax->addr is just bogus > (which is what I currently believe since I see no way how the address > could > be unaligned with the sector_size)... > Good catch, and you're right. I don't think I actually even want to use dax->addr for the alignment check here - I want to check if we're aligned to the block device sector. I'm thinking something like: if (!IS_ALIGNED(offset, sector_size)) Technically we want to check if sector * sector_size + offset is aligned, but the first part of that is already a sector :)
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..0167cde 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 (!IS_ALIGNED(((u64)dax->addr + offset), sector_size)) + return false; + if (!IS_ALIGNED(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 +1254,16 @@ 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 >> 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;