On 11/12/19 5:35 PM, Dan Williams wrote:
On Tue, Nov 12, 2019 at 5:08 PM John Hubbard jhubbard@nvidia.com wrote:
On 11/12/19 4:58 PM, Dan Williams wrote: ...
It's not redundant relative to upstream which does not do anything the FOLL_LONGTERM in the gup-slow path... but I have not looked at patches 1-7 to see if something there made it redundant.
Oh, the hunk John had below for get_user_pages_remote() also needs to call __gup_longterm_locked() when FOLL_LONGTERM is specified, then that calls check_dax_vmas() which duplicates the vma_is_fsdax() check above.
Oh true, good eye. It is redundant if it does additionally call __gup_longterm_locked(), and it needs to do that otherwises it undoes the CMA migration magic that Aneesh added.
OK. So just to be clear, I'll be removing this from the patch:
/* * The lifetime of a vaddr_get_pfn() page pin is * userspace-controlled. In the fs-dax case this could * lead to indefinite stalls in filesystem operations. * Disallow attempts to pin fs-dax pages via this * interface. */ if (ret > 0 && vma_is_fsdax(vmas[0])) { ret = -EOPNOTSUPP; put_page(page[0]); }(and the declaration of "vmas", as well).
...and add a call to __gup_longterm_locked internal to get_user_pages_remote(), right?
Yes, and thanks for double-checking. I think I got a little dizzy following the call stack there. :) And now I see that this also affects the implementation of pin_longterm_pages_remote(), because that will need the same logic that get_user_pages_remote() has.
thanks,