On Tue, Nov 12, 2019 at 10:10 PM John Hubbard jhubbard@nvidia.com wrote:
On 11/12/19 12:38 PM, Jason Gunthorpe wrote:
On Mon, Nov 11, 2019 at 04:06:37PM -0800, John Hubbard wrote:
Hi,
The cover letter is long, so the more important stuff is first:
Jason, if you or someone could look at the the VFIO cleanup (patch 8) and conversion to FOLL_PIN (patch 18), to make sure it's use of remote and longterm gup matches what we discussed during the review of v2, I'd appreciate it.
Also for Jason and IB: as noted below, in patch 11, I am (too?) boldly converting from put_user_pages() to release_pages().
Why are we doing this? I think things got confused here someplace, as
Because:
a) These need put_page() calls, and
b) there is no put_pages() call, but there is a release_pages() call that is, arguably, what put_pages() would be.
the comment still says:
/**
- put_user_page() - release a gup-pinned page
- @page: pointer to page to be released
- Pages that were pinned via get_user_pages*() must be released via
- either put_user_page(), or one of the put_user_pages*() routines
- below.
Ohhh, I missed those comments. They need to all be changed over to say "pages that were pinned via pin_user_pages*() or pin_longterm_pages*() must be released via put_user_page*()."
The get_user_pages*() pages must still be released via put_page.
The churn is due to a fairly significant change in strategy, whis is: instead of changing all get_user_pages*() sites to call put_user_page(), change selected sites to call pin_user_pages*() or pin_longterm_pages*(), plus put_user_page().
Can't we call this unpin_user_page then, for some symmetry? Or is that even more churn?
Looking from afar the naming here seems really confusing. -Daniel
That allows incrementally converting the kernel over to using the new pin APIs, without taking on the huge risk of a big one-shot conversion.
So, I've ended up with one place that actually needs to get reverted back to get_user_pages(), and that's the IB ODP code.
I feel like if put_user_pages() is not the correct way to undo get_user_pages() then it needs to be deleted.
Yes, you're right. I'll fix the put_user_page comments() as described.
thanks,
John Hubbard NVIDIA