linux-kernel - Re: [PATCH] mm/Kconfig: additional help text for HMM

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Date:   Fri, 19 Jul 2019 12:52:39 +0200
From:   Pavel Machek <pavel@....cz>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     john.hubbard@...il.com, SCheung@...dia.com,
        akpm@...ux-foundation.org, aneesh.kumar@...ux.vnet.ibm.com,
        benh@...nel.crashing.org, bsingharora@...il.com,
        dan.j.williams@...el.com, dnellans@...dia.com,
        ebaskakov@...dia.com, hannes@...xchg.org, jglisse@...hat.com,
        jhubbard@...dia.com, kirill.shutemov@...ux.intel.com,
        linux-kernel@...r.kernel.org, liubo95@...wei.com,
        mhairgrove@...dia.com, mhocko@...nel.org,
        paulmck@...ux.vnet.ibm.com, ross.zwisler@...ux.intel.com,
        sgutti@...dia.com, torvalds@...ux-foundation.org,
        vdavydov.dev@...il.com, Jason Gunthorpe <jgg@...pe.ca>
Subject: Re: [PATCH] mm/Kconfig: additional help text for HMM_MIRROR option

On Thu 2019-07-18 22:57:48, Christoph Hellwig wrote:
> On Thu, Jul 18, 2019 at 06:32:53PM -0700, john.hubbard@...il.com wrote:
> > +	  HMM_MIRROR provides a way to mirror ranges of the CPU page tables
> > +	  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.
> > +
> > +	  Select HMM_MIRROR if you have hardware that meets the above
> > +	  description. An early, partial list of such hardware is:
> > +	  an NVIDIA GPU >= Pascal, Mellanox IB >= mlx5, or an AMD GPU.
> 
> Nevermind that the Nvidia support is stagaging and looks rather broken,
> there is no Mellanox user of this either at this point.
> 
> But either way this has no business in a common kconfig help.  Just
> drop the fine grained details and leave it to the overview.

I disagree here. This explains what kind of hardware this is for (very
new). Partial list does not hurt, and I know that I probably don't
need to enable this.

How else am I supposed to know if my computer needs page tables
synchronized?

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

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