linux-kernel - Re: [RFC PATCH 2/2] mm/gup: introduce vaddr_pin_pages

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Date:   Fri, 16 Aug 2019 17:41:08 +0200
From:   Jan Kara <jack@...e.cz>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     Ira Weiny <ira.weiny@...el.com>, Jan Kara <jack@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Hellwig <hch@...radead.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Jérôme Glisse <jglisse@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-rdma@...r.kernel.org
Subject: Re: [RFC PATCH 2/2] mm/gup: introduce vaddr_pin_pages_remote()

On Thu 15-08-19 19:14:08, John Hubbard wrote:
> On 8/15/19 10:41 AM, John Hubbard wrote:
> > On 8/15/19 10:32 AM, Ira Weiny wrote:
> >> On Thu, Aug 15, 2019 at 03:35:10PM +0200, Jan Kara wrote:
> >>> On Thu 15-08-19 15:26:22, Jan Kara wrote:
> >>>> On Wed 14-08-19 20:01:07, John Hubbard wrote:
> >>>>> On 8/14/19 5:02 PM, John Hubbard wrote:
> ...
> >> Ok just to make this clear I threw up my current tree with your patches here:
> >>
> >> https://github.com/weiny2/linux-kernel/commits/mmotm-rdmafsdax-b0-v4
> >>
> >> I'm talking about dropping the final patch:
> >> 05fd2d3afa6b rdma/umem_odp: Use vaddr_pin_pages_remote() in ODP
> >>
> >> The other 2 can stay.  I split out the *_remote() call.  We don't have a user
> >> but I'll keep it around for a bit.
> >>
> >> This tree is still WIP as I work through all the comments.  So I've not changed
> >> names or variable types etc...  Just wanted to settle this.
> >>
> > 
> > Right. And now that ODP is not a user, I'll take a quick look through my other
> > call site conversions and see if I can find an easy one, to include here as
> > the first user of vaddr_pin_pages_remote(). I'll send it your way if that
> > works out.
> > 
> 
> OK, there was only process_vm_access.c, plus (sort of) Bharath's sgi-gru
> patch, maybe eventually [1].  But looking at process_vm_access.c, I think 
> it is one of the patches that is no longer applicable, and I can just
> drop it entirely...I'd welcome a second opinion on that...

I don't think you can drop the patch. process_vm_rw_pages() clearly touches
page contents and does not synchronize with page_mkclean(). So it is case
1) and needs FOLL_PIN semantics.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR