On Mon, Nov 04, 2019 at 02:03:43PM -0800, John Hubbard wrote:
> On 11/4/19 12:57 PM, Jason Gunthorpe wrote:
> > On Mon, Nov 04, 2019 at 12:48:13PM -0800, John Hubbard wrote:
> >> On 11/4/19 12:33 PM, Jason Gunthorpe wrote:
> >> ...
> >>>> diff --git a/drivers/infiniband/core/umem.c
> >>>> b/drivers/infiniband/core/umem.c
> >>>> index 24244a2f68cc..c5a78d3e674b 100644
> >>>> +++ b/drivers/infiniband/core/umem.c
> >>>> @@ -272,11 +272,10 @@ struct ib_umem *ib_umem_get(struct ib_udata
> >>>> *udata, unsigned long addr,
> >>>>
> >>>> while (npages) {
> >>>> down_read(&mm->mmap_sem);
> >>>> - ret = get_user_pages(cur_base,
> >>>> + ret = pin_longterm_pages(cur_base,
> >>>> min_t(unsigned long, npages,
> >>>> PAGE_SIZE / sizeof (struct
> >>>> page *)),
> >>>> - gup_flags | FOLL_LONGTERM,
> >>>> - page_list, NULL);
> >>>> + gup_flags, page_list, NULL);
> >>>
> >>> FWIW, this one should be converted to fast as well, I think we finally
> >>> got rid of all the blockers for that?
> >>>
> >>
> >> I'm not aware of any blockers on the gup.c end, anyway. The only broken
> >> thing we
> >> have there is "gup remote + FOLL_LONGTERM". But we can do "gup fast +
> >> LONGTERM".
> >
> > I mean the use of the mmap_sem here is finally in a way where we can
> > just delete the mmap_sem and use _fast
> >
> > ie, AFAIK there is no need for the mmap_sem to be held during
> > ib_umem_add_sg_table()
> >
> > This should probably be a standalone patch however
> >
>
> Yes. Oh, actually I guess the patch flow should be: change to
> get_user_pages_fast() and remove the mmap_sem calls, as one patch. And then
> change
> to pin_longterm_pages_fast() as the next patch. Otherwise, the internal
> fallback
> from _fast to slow gup would attempt to take the mmap_sem (again) in the same
> thread, which is not good. :)
>
> Or just defer the change until after this series. Either way is fine, let me
> know if you prefer one over the other.
>
> The patch itself is trivial, but runtime testing to gain confidence that
> it's solid is much harder. Is there a stress test you would recommend for
> that?
> (I'm not promising I can quickly run it yet--my local IB setup is still
> nascent
> at best.)
If you make a patch we can probably get it tested, it is something
we should do I keep forgetting about.
Jason
