[Intel-gfx] [PATCH hmm v2 2/5] mm/hmm: make hmm_range_fault return 0 or -1
jhubbard at nvidia.com
Tue May 5 00:20:58 UTC 2020
On 2020-05-01 11:20, Jason Gunthorpe wrote:
> From: Jason Gunthorpe <jgg at mellanox.com>
> hmm_vma_walk->last is supposed to be updated after every write to the
> pfns, so that it can be returned by hmm_range_fault(). However, this is
> not done consistently. Fortunately nothing checks the return code of
> hmm_range_fault() for anything other than error.
> More importantly last must be set before returning -EBUSY as it is used to
> prevent reading an output pfn as an input flags when the loop restarts.
> For clarity and simplicity make hmm_range_fault() return 0 or -ERRNO. Only
> set last when returning -EBUSY.
Yes, this is also a nice simplification.
> @@ -590,10 +580,13 @@ long hmm_range_fault(struct hmm_range *range)
> return -EBUSY;
> ret = walk_page_range(mm, hmm_vma_walk.last, range->end,
> &hmm_walk_ops, &hmm_vma_walk);
> + /*
> + * When -EBUSY is returned the loop restarts with
> + * hmm_vma_walk.last set to an address that has not been stored
> + * in pfns. All entries < last in the pfn array are set to their
> + * output, and all >= are still at their input values.
> + */
I'm glad you added that comment. This is much easier to figure out with
that in place. After poking around this patch and eventually understanding the
.last handling, I wondered if you might like this slightly tweaked wording
* Each of the hmm_walk_ops routines returns -EBUSY if and only
* hmm_vma_walk.last has been set to an address that has not yet
* been stored in pfns. All entries < last in the pfn array are
* set to their output, and all >= are still at their input
Reviewed-by: John Hubbard <jhubbard at nvidia.com>
> } while (ret == -EBUSY);
> - if (ret)
> - return ret;
> - return (hmm_vma_walk.last - range->start) >> PAGE_SHIFT;
> + return ret;
More information about the Intel-gfx