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SubjectRe: [PATCH 3/4] infiniband/mm: convert to the new put_user_page() call
On Fri, Sep 28, 2018 at 08:12:33PM -0700, John Hubbard wrote:
> >> +++ 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.

I think our current interfaces are wrong. We should really have a
get_user_sg() / put_user_sg() function that will set up / destroy an
SG list appropriate for that range of user memory. This is almost
orthogonal to the original intent here, so please don't see this as a
"must do first" kind of argument that might derail the whole thing.

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