Re: [RFC PATCH 2/2] mm/gup: introduce vaddr_pin_pages_remote()
From: Ira Weiny
Date: Fri Aug 16 2019 - 18:00:26 EST
On Fri, Aug 16, 2019 at 11:50:09AM -0700, John Hubbard wrote:
> On 8/16/19 11:33 AM, Ira Weiny wrote:
> > On Fri, Aug 16, 2019 at 05:41:08PM +0200, Jan Kara wrote:
> > > 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, there was only process_vm_access.c, plus (sort of) Bharath's sgi-gru
> > > > patch, maybe eventually . 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 it is one of the patches that is no longer applicable, and I can just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.
> > John could you send a formal patch using vaddr_pin* and I'll add it to the
> > tree?
> Yes...hints about which struct file to use here are very welcome, btw. This part
> of mm is fairly new to me.
I'm still working out the final semantics of vaddr_pin*. But right now you
don't need a vaddr_pin if you don't specify FOLL_LONGTERM.
Since case 1, this case, does not need FOLL_LONGTERM I think it is safe to
simply pass NULL here.
OTOH we could just track this against the mm_struct. But I don't think we need
to because this pin should be transient.
And this is why I keep leaning toward _not_ putting these flags in the
vaddr_pin*() calls. I know this is what I did but I think I'm wrong. It should
be the caller specifying what they want and the vaddr_pin*() calls check that
what they are asking for is correct.
> John Hubbard