On 3/22/2022 2:01 AM, Christoph Hellwig wrote:
> On Sat, Mar 19, 2022 at 12:28:31AM -0600, Jane Chu wrote:
>> Introduce DAX_RECOVERY flag to dax_direct_access(). The flag is
>> not set by default in dax_direct_access() such that the helper
>> does not translate a pmem range to kernel virtual address if the
>> range contains uncorrectable errors. When the flag is set,
>> the helper ignores the UEs and return kernel virtual adderss so
>> that the caller may get on with data recovery via write.
>
> This DAX_RECOVERY doesn't actually seem to be used anywhere here or
> in the subsequent patches. Did I miss something?
dax_iomap_iter() uses the flag in the same patch,
+ if ((map_len == -EIO) && (iov_iter_rw(iter) == WRITE)) {
+ flags |= DAX_RECOVERY;
+ map_len = dax_direct_access(dax_dev, pgoff, nrpg,
+ flags, &kaddr, NULL);
>
>> Also introduce a new dev_pagemap_ops .recovery_write function.
>> The function is applicable to FSDAX device only. The device
>> page backend driver provides .recovery_write function if the
>> device has underlying mechanism to clear the uncorrectable
>> errors on the fly.
>
> Why is this not in struct dax_operations?
Per Dan's comments to the v5 series, adding .recovery_write to
dax_operations causes a number of trivial dm targets changes.
Dan suggested that adding .recovery_write to pagemap_ops could
cut short the logistics of figuring out whether the driver backing
up a page is indeed capable of clearing poison. Please see
https://lkml.org/lkml/2022/2/4/31
>
>>
>> +size_t dax_recovery_write(struct dax_device *dax_dev, pgoff_t pgoff,
>> + void *addr, size_t bytes, struct iov_iter *iter)
>> +{
>> + struct dev_pagemap *pgmap = dax_dev->pgmap;
>> +
>> + if (!pgmap || !pgmap->ops->recovery_write)
>> + return -EIO;
>> + return pgmap->ops->recovery_write(pgmap, pgoff, addr, bytes,
>> + (void *)iter);
>
> No need to cast a type pointer to a void pointer. But more importantly
> losing the type information here and passing it as void seems very
> wrong.
include/linux/memremap.h doesn't know struct iov_iter which is defined
in include/linux/uio.h, would you prefer to adding include/linux/uio.h
to include/linux/memremap.h ?
>
>> +static size_t pmem_recovery_write(struct dev_pagemap *pgmap, pgoff_t pgoff,
>> + void *addr, size_t bytes, void *iter)
>> +{
>> + struct pmem_device *pmem = pgmap->owner;
>> +
>> + dev_warn(pmem->bb.dev, "%s: not yet implemented\n", __func__);
>> +
>> + /* XXX more later */
>> + return 0;
>> +}
>
> This shuld not be added here - the core code can cope with a NULL
> method just fine.
Okay, will remove the XXX line.
>
>> + recov = 0;
>> + flags = 0;
>> + nrpg = PHYS_PFN(size);
>
> Please spell out the words. The recovery flag can also be
> a bool to make the code more readable.
Sure.
>
>> + map_len = dax_direct_access(dax_dev, pgoff, nrpg, flags,
>> + &kaddr, NULL);
>> + if ((map_len == -EIO) && (iov_iter_rw(iter) == WRITE)) {
>
> No need for the inner braces.
Okay.
>
>> + flags |= DAX_RECOVERY;
>> + map_len = dax_direct_access(dax_dev, pgoff, nrpg,
>> + flags, &kaddr, NULL);
>
> And noneed for the flags variable at all really.
Okay.
>
>> xfer = dax_copy_from_iter(dax_dev, pgoff, kaddr,
>> map_len, iter);
>> else
>> @@ -1271,6 +1286,11 @@ static loff_t dax_iomap_iter(const struct iomap_iter *iomi,
>> length -= xfer;
>> done += xfer;
>>
>> + if (recov && (xfer == (ssize_t) -EIO)) {
>> + pr_warn("dax_recovery_write failed\n");
>> + ret = -EIO;
>> + break;
>
> And no, we can't just use an unsigned variable to communicate a
> negative error code.
Okay, will have dax_recovery_write return 0 in all error cases.
thanks!
-jane
