linux-kernel - Re: HMM_MIRROR has less than useful help text

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Message-ID: <20190718163601.GA21502@amd>
Date:   Thu, 18 Jul 2019 18:36:01 +0200
From:   Pavel Machek <pavel@....cz>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Balbir Singh <bsingharora@...il.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Evgeny Baskakov <ebaskakov@...dia.com>,
        John Hubbard <jhubbard@...dia.com>,
        Mark Hairgrove <mhairgrove@...dia.com>,
        Sherry Cheung <SCheung@...dia.com>,
        Subhash Gutti <sgutti@...dia.com>,
        Aneesh Kumar KV <aneesh.kumar@...ux.vnet.ibm.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        David Nellans <dnellans@...dia.com>,
        Johannes Weiner <hannes@...xchg.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Michal Hocko <mhocko@...nel.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Bob Liu <liubo95@...wei.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        kernel list <linux-kernel@...r.kernel.org>
Subject: Re: HMM_MIRROR has less than useful help text

On Thu 2019-07-18 07:25:42, Dan Williams wrote:
> On Thu, Jul 18, 2019 at 4:04 AM Balbir Singh <bsingharora@...il.com> wrote:
> >
> > On Wed, Jul 17, 2019 at 5:41 PM Pavel Machek <pavel@....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?

I hoped patch author would fix up their code. I'm not HMM expert, he
should be...

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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