On Thu, Jan 23, 2020 at 11:52:49AM -0500, Vivek Goyal wrote:
> Hi,
>
> This is an RFC patch to provide a dax operation to zero a range of memory.
> It will also clear poison in the process. This is primarily compile tested
> patch. I don't have real hardware to test the poison logic. I am posting
> this to figure out if this is the right direction or not.
>
> Motivation from this patch comes from Christoph's feedback that he will
> rather prefer a dax way to zero a range instead of relying on having to
> call blkdev_issue_zeroout() in __dax_zero_page_range().
>
> https://lkml.org/lkml/2019/8/26/361
>
> My motivation for this change is virtiofs DAX support. There we use DAX
> but we don't have a block device. So any dax code which has the assumption
> that there is always a block device associated is a problem. So this
> is more of a cleanup of one of the places where dax has this dependency
> on block device and if we add a dax operation for zeroing a range, it
> can help with not having to call blkdev_issue_zeroout() in dax path.
>
> I have yet to take care of stacked block drivers (dm/md).
>
> Current poison clearing logic is primarily written with assumption that
> I/O is sector aligned. With this new method, this assumption is broken
> and one can pass any range of memory to zero. I have fixed few places
> in existing logic to be able to handle an arbitrary start/end. I am
> not sure are there other dependencies which might need fixing or
> prohibit us from providing this method.
>
> Any feedback or comment is welcome.
>
> Thanks
> Vivek
>
> ---
> drivers/dax/super.c | 13 +++++++++
> drivers/nvdimm/pmem.c | 67
> ++++++++++++++++++++++++++++++++++++++++++--------
> fs/dax.c | 39 ++++++++---------------------
> include/linux/dax.h | 3 ++
> 4 files changed, 85 insertions(+), 37 deletions(-)
>
> Index: rhvgoyal-linux/drivers/nvdimm/pmem.c
> ===================================================================
> --- rhvgoyal-linux.orig/drivers/nvdimm/pmem.c 2020-01-23 11:32:11.075139183
> -0500
> +++ rhvgoyal-linux/drivers/nvdimm/pmem.c 2020-01-23 11:32:28.660139183
> -0500
> @@ -52,8 +52,8 @@ static void hwpoison_clear(struct pmem_d
> if (is_vmalloc_addr(pmem->virt_addr))
> return;
>
> - pfn_start = PHYS_PFN(phys);
> - pfn_end = pfn_start + PHYS_PFN(len);
> + pfn_start = PFN_UP(phys);
> + pfn_end = PFN_DOWN(phys + len);
> for (pfn = pfn_start; pfn < pfn_end; pfn++) {
> struct page *page = pfn_to_page(pfn);
>
This change looks unrelated to the rest.
> + sector_end = ALIGN_DOWN((offset - pmem->data_offset + len), 512)/512;
> + nr_sectors = sector_end - sector_start;
>
> cleared = nvdimm_clear_poison(dev, pmem->phys_addr + offset, len);
> if (cleared < len)
> rc = BLK_STS_IOERR;
> - if (cleared > 0 && cleared / 512) {
> + if (cleared > 0 && nr_sectors > 0) {
> hwpoison_clear(pmem, pmem->phys_addr + offset, cleared);
> - cleared /= 512;
> - dev_dbg(dev, "%#llx clear %ld sector%s\n",
> - (unsigned long long) sector, cleared,
> - cleared > 1 ? "s" : "");
> - badblocks_clear(&pmem->bb, sector, cleared);
> + dev_dbg(dev, "%#llx clear %d sector%s\n",
> + (unsigned long long) sector_start, nr_sectors,
> + nr_sectors > 1 ? "s" : "");
> + badblocks_clear(&pmem->bb, sector_start, nr_sectors);
> if (pmem->bb_state)
> sysfs_notify_dirent(pmem->bb_state);
> }
As does this one?
> int __dax_zero_page_range(struct block_device *bdev,
> struct dax_device *dax_dev, sector_t sector,
> unsigned int offset, unsigned int size)
> {
> + pgoff_t pgoff;
> + long rc, id;
>
> + rc = bdev_dax_pgoff(bdev, sector, PAGE_SIZE, &pgoff);
> + if (rc)
> + return rc;
> +
> + id = dax_read_lock();
> + rc = dax_zero_page_range(dax_dev, pgoff, offset, size);
> + if (rc == -EOPNOTSUPP) {
> void *kaddr;
>
> + /* If driver does not implement zero page range, fallback */
I think we'll want to restructure this a bit. First make the new
method mandatory, and just provide a generic_dax_zero_page_range or
similar for the non-pmem instances.
Then __dax_zero_page_range and iomap_dax_zero should merge, and maybe
eventually iomap_zero_range_actor and iomap_zero_range should be split
into a pagecache and DAX variant, lifting the IS_DAXD check into the
callers.
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