Re: [PATCH v2] infiniband/mm: convert put_page() to put_user_page*()

Jason Gunthorpe
2019-05-27T22:57:03Z

On Sun, May 26, 2019 at 04:06:31AM -0700, Matthew Wilcox wrote:
> On Fri, May 24, 2019 at 06:45:22PM -0700, john.hubbard@gmail.com wrote:
> > For infiniband code that retains pages via get_user_pages*(),
> > release those pages via the new put_user_page(), or
> > put_user_pages*(), instead of put_page()
>
> I have no objection to this particular patch, but ...
>
> > This is a tiny part of the second step of fixing the problem described
> > in [1]. The steps are:
> >
> > 1) Provide put_user_page*() routines, intended to be used
> > for releasing pages that were pinned via get_user_pages*().
> >
> > 2) Convert all of the call sites for get_user_pages*(), to
> > invoke put_user_page*(), instead of put_page(). This involves dozens of
> > call sites, and will take some time.
> >
> > 3) After (2) is complete, use get_user_pages*() and put_user_page*() to
> > implement tracking of these pages. This tracking will be separate from
> > the existing struct page refcounting.
> >
> > 4) Use the tracking and identification of these pages, to implement
> > special handling (especially in writeback paths) when the pages are
> > backed by a filesystem. Again, [1] provides details as to why that is
> > desirable.
>
> I thought we agreed at LSFMM that the future is a new get_user_bvec()
> / put_user_bvec(). This is largely going to touch the same places as
> step 2 in your list above. Is it worth doing step 2?

I think so, as these two conversions can run in parallel, whichever we
finish first, biovec or put_user_pages lets John progress to step #3

Jason