Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
References: <20190717074124.GA21617@amd> <CAKTCnzkzvPgMK8i-cTuWFLRPPg4=DTkVQmS238VTgYJaUy=iVA@mail.gmail.com>
In-Reply-To: <CAKTCnzkzvPgMK8i-cTuWFLRPPg4=DTkVQmS238VTgYJaUy=iVA@mail.gmail.com>
From:   Dan Williams <dan.j.williams@intel.com>
Date:   Thu, 18 Jul 2019 07:25:42 -0700
Message-ID: <CAPcyv4i3vzuWfKQXF-GWKpCXACjE6HTeczPRoHUp+tOBMEAP-Q@mail.gmail.com>
Subject: Re: HMM_MIRROR has less than useful help text
To:     Balbir Singh <bsingharora@gmail.com>
Cc:     Pavel Machek <pavel@ucw.cz>,
        =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= <jglisse@redhat.com>,
        Evgeny Baskakov <ebaskakov@nvidia.com>,
        John Hubbard <jhubbard@nvidia.com>,
        Mark Hairgrove <mhairgrove@nvidia.com>,
        Sherry Cheung <SCheung@nvidia.com>,
        Subhash Gutti <sgutti@nvidia.com>,
        Aneesh Kumar KV <aneesh.kumar@linux.vnet.ibm.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        David Nellans <dnellans@nvidia.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Michal Hocko <mhocko@kernel.org>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Ross Zwisler <ross.zwisler@linux.intel.com>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Bob Liu <liubo95@huawei.com>,
        "akpm@linux-foundation.org" <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        kernel list <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Thu, Jul 18, 2019 at 4:04 AM Balbir Singh <bsingharora@gmail.com> wrote:
>
> On Wed, Jul 17, 2019 at 5:41 PM Pavel Machek <pavel@ucw.cz> wrote:
> >
> > Hi!
> >
> > Commit c0b124054f9e42eb6da545a10fe9122a7d7c3f72 has very nice commit
> > message, explaining what HMM_MIRROR is and when it is
> > needed. Unfortunately, it did not make it into Kconfig help:
> >
> > CONFIG_HMM_MIRROR:
> >
> > Select HMM_MIRROR if you want to mirror range of the CPU page table of
> > a
> > process into a device page table. Here, mirror means "keep
> > synchronized".
> > Prerequisites: the device must provide the ability to write-protect
> > its
> > page tables (at PAGE_SIZE granularity), and must be able to recover
> > from
> > the resulting potential page faults.
> >
> > Could that be fixed?
> >
> > This is key information for me:
> >
> > # This is a heterogeneous memory management (HMM) process address space
> > # mirroring.
> > # This is useful for NVidia GPU >= Pascal, Mellanox IB >= mlx5 and more
> > # hardware in the future.
> >
>
> That seems like a reasonable request

Hi Pavel, care to send a patch?