Re: [PATCH 3/4] infiniband/mm: convert to the new put_user_page() call

[Dennis Dalessandro]

On 9/28/2018 11:12 PM, John Hubbard wrote:
> On 9/28/18 8:39 AM, Jason Gunthorpe wrote:
> > On Thu, Sep 27, 2018 at 10:39:47PM -0700, john.hubbard@xxxxxxxxx wrote:
> > > From: John Hubbard <jhubbard@xxxxxxxxxx>
> [...]
> > > diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c
> > > index a41792dbae1f..9430d697cb9f 100644
> > > +++ b/drivers/infiniband/core/umem.c
> > > @@ -60,7 +60,7 @@ static void __ib_umem_release(struct ib_device *dev, struct ib_umem *umem, int d
> > >   		page = sg_page(sg);
> > >   		if (!PageDirty(page) && umem->writable && dirty)
> > >   			set_page_dirty_lock(page);
> > > -		put_page(page);
> > > +		put_user_page(page);
> >
> > Would it make sense to have a release/put_user_pages_dirtied to absorb
> > the set_page_dity pattern too? I notice in this patch there is some
> > variety here, I wonder what is the right way?
> >
> > Also, I'm told this code here is a big performance bottleneck when the
> > number of pages becomes very long (think >> GB of memory), so having a
> > future path to use some kind of batching/threading sound great.
>
> Yes. And you asked for this the first time, too. Consistent! :) Sorry for
> being slow to pick it up. It looks like there are several patterns, and
> we have to support both set_page_dirty() and set_page_dirty_lock(). So
> the best combination looks to be adding a few variations of
> release_user_pages*(), but leaving put_user_page() alone, because it's
> the "do it yourself" basic one. Scatter-gather will be stuck with that.
>
> Here's a differential patch with that, that shows a nice little cleanup in
> a couple of IB places, and as you point out, it also provides the hooks for
> performance upgrades (via batching) in the future.
>
> Does this API look about right?

I'm on board with that and the changes to hfi1 and qib.

Reviewed-by: Dennis Dalessandro <dennis.dalessandro@xxxxxxxxx>