Re: [PATCH v3 0/2] iov_iter: allow iov_iter_get_pages_alloc to allocate more pages per call

From: Jeff Layton
Date: Thu Feb 16 2017 - 08:10:39 EST

On Thu, 2017-02-02 at 09:51 +0000, Al Viro wrote:
> On Wed, Jan 25, 2017 at 08:32:03AM -0500, Jeff Layton wrote:
> > Small respin of the patch that I sent yesterday for the same thing.
> >
> > This moves the maxsize handling into iov_iter_pvec_size, so that we don't
> > end up iterating past the max size we'll use anyway when trying to
> > determine the pagevec length.
> >
> > Also, a respun patch to make ceph use iov_iter_get_pages_alloc instead of
> > trying to do it via its own routine.
> >
> > Al, if these look ok, do you want to pick these up or shall I ask
> > Ilya to merge them via the ceph tree?
> I'd rather have that kind of work go through the vfs tree; said that,
> I really wonder if this is the right approach. Most of the users of
> iov_iter_get_pages()/iov_iter_get_pages_alloc() look like they want
> something like
> iov_iter_for_each_page(iter, size, f, data)
> with int (*f)(struct page *page, size_t from, size_t size, void *data)
> passed as callback. Not everything fits that model, but there's a whole
> lot of things that do.

While I do like the above proposal better than what I originally had,
I'm guessing it won't be ready in time for v4.11.

Would it be reasonable to take the patch I proposed for v4.11 as an
interim fix? It does fix a rather easy-to-trigger softlockup in the ceph
code that xfstests can reliably hit.

Jeff Layton <jlayton@xxxxxxxxxx>