From: Peter Xu <peterx@redhat.com>
To: John Hubbard <jhubbard@nvidia.com>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Paolo Bonzini <pbonzini@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
David Hildenbrand <david@redhat.com>,
"Dr . David Alan Gilbert" <dgilbert@redhat.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Linux MM Mailing List <linux-mm@kvack.org>,
Sean Christopherson <seanjc@google.com>
Subject: Re: [PATCH 1/4] mm/gup: Add FOLL_INTERRUPTIBLE
Date: Tue, 28 Jun 2022 18:33:50 -0400 [thread overview]
Message-ID: <YruBzuJf9s/Nmr6W@xz-m1.local> (raw)
In-Reply-To: <16c181d3-09ef-ace4-c910-0a13fc245e48@nvidia.com>
On Tue, Jun 28, 2022 at 02:40:53PM -0700, John Hubbard wrote:
> On 6/28/22 12:31, Peter Xu wrote:
> > > > diff --git a/mm/gup.c b/mm/gup.c
> > > > index 551264407624..ad74b137d363 100644
> > > > --- a/mm/gup.c
> > > > +++ b/mm/gup.c
> > > > @@ -933,8 +933,17 @@ static int faultin_page(struct vm_area_struct *vma,
> > > > fault_flags |= FAULT_FLAG_WRITE;
> > > > if (*flags & FOLL_REMOTE)
> > > > fault_flags |= FAULT_FLAG_REMOTE;
> > > > - if (locked)
> > > > + if (locked) {
> > > > fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
> > > > + /*
> > > > + * We should only grant FAULT_FLAG_INTERRUPTIBLE when we're
> > > > + * (at least) killable. It also mostly means we're not
> > > > + * with NOWAIT. Otherwise ignore FOLL_INTERRUPTIBLE since
> > > > + * it won't make a lot of sense to be used alone.
> > > > + */
> > >
> > > This comment seems a little confusing due to its location. We've just
> > > checked "locked", but the comment is talking about other constraints.
> > >
> > > Not sure what to suggest. Maybe move it somewhere else?
> >
> > I put it here to be after FAULT_FLAG_KILLABLE we just set.
> >
> > Only if we have "locked" will we set FAULT_FLAG_KILLABLE. That's also the
> > key we grant "killable" attribute to this GUP. So I thought it'll be good
> > to put here because I want to have FOLL_INTERRUPTIBLE dependent on "locked"
> > being set.
> >
>
> The key point is the connection between "locked" and killable. If the comment
> explained why "locked" means "killable", that would help clear this up. The
> NOWAIT sentence is also confusing to me, and adding "mostly NOWAIT" does not
> clear it up either... :)
Sorry to have a comment that makes it feels confusing. I tried to
explicitly put the comment to be after setting FAULT_FLAG_KILLABLE but
obviously I didn't do my job well..
Maybe that NOWAIT thing adds more complexity but not even necessary.
Would below one more acceptable?
/*
* We'll only be able to respond to signals when "locked !=
* NULL". When with it, we'll always respond to SIGKILL
* (as implied by FAULT_FLAG_KILLABLE above), and we'll
* respond to non-fatal signals only if the GUP user has
* specified FOLL_INTERRUPTIBLE.
*/
Thanks,
--
Peter Xu
next prev parent reply other threads:[~2022-06-28 22:34 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-22 21:36 [PATCH 0/4] kvm/mm: Allow GUP to respond to non fatal signals Peter Xu
2022-06-22 21:36 ` [PATCH 1/4] mm/gup: Add FOLL_INTERRUPTIBLE Peter Xu
2022-06-25 0:35 ` Jason Gunthorpe
2022-06-25 1:23 ` Peter Xu
2022-06-25 23:59 ` Jason Gunthorpe
2022-06-27 15:29 ` Peter Xu
2022-06-28 2:07 ` John Hubbard
2022-06-28 19:31 ` Peter Xu
2022-06-28 21:40 ` John Hubbard
2022-06-28 22:33 ` Peter Xu [this message]
2022-06-29 0:31 ` John Hubbard
2022-06-29 15:47 ` Peter Xu
2022-06-30 1:53 ` John Hubbard
2022-06-30 13:49 ` Peter Xu
2022-06-30 19:01 ` John Hubbard
2022-06-30 21:27 ` Peter Xu
2022-07-04 22:48 ` Matthew Wilcox
2022-07-07 15:06 ` Peter Xu
2022-06-22 21:36 ` [PATCH 2/4] kvm: Merge "atomic" and "write" in __gfn_to_pfn_memslot() Peter Xu
2022-06-23 14:49 ` Sean Christopherson
2022-06-23 19:46 ` Peter Xu
2022-06-23 20:29 ` Sean Christopherson
2022-06-23 21:29 ` Peter Xu
2022-06-23 21:52 ` Sean Christopherson
2022-06-27 19:12 ` John Hubbard
2022-06-28 2:17 ` John Hubbard
2022-06-28 19:46 ` Peter Xu
2022-06-28 21:52 ` John Hubbard
2022-06-28 22:50 ` Peter Xu
2022-06-28 22:55 ` John Hubbard
2022-06-28 23:02 ` Peter Xu
2022-06-22 21:36 ` [PATCH 3/4] kvm: Add new pfn error KVM_PFN_ERR_INTR Peter Xu
2022-06-23 14:31 ` Sean Christopherson
2022-06-23 19:32 ` Peter Xu
2022-06-22 21:36 ` [PATCH 4/4] kvm/x86: Allow to respond to generic signals during slow page faults Peter Xu
2022-06-23 14:46 ` Sean Christopherson
2022-06-23 19:31 ` Peter Xu
2022-06-23 20:07 ` Sean Christopherson
2022-06-23 20:18 ` Peter Xu
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