linux-kernel - Re: [PATCH v4 2/2] mm/gup/writeback: add callbacks for inaccessible pages

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Date:   Tue, 28 Apr 2020 17:42:20 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Claudio Imbrenda <imbrenda@...ux.ibm.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>, linux-next@...r.kernel.org,
        akpm@...ux-foundation.org, jack@...e.cz, kirill@...temov.name,
        "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        borntraeger@...ibm.com, david@...hat.com, aarcange@...hat.com,
        linux-mm@...ck.org, frankja@...ux.ibm.com, sfr@...b.auug.org.au,
        jhubbard@...dia.com, linux-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org, Will Deacon <will@...nel.org>,
        "Williams, Dan J" <dan.j.williams@...el.com>, pasic@...ux.ibm.com
Subject: Re: [PATCH v4 2/2] mm/gup/writeback: add callbacks for inaccessible
 pages

On 4/28/20 4:39 PM, Claudio Imbrenda wrote:
>> From where I'm standing, we have a hook in the core VM that can't
>> possibly work with some existing kernel functionality and has
>> virtually no chance of getting used on a second architecture.
> it seems to work at least for us, so it does possibly work :)

I think all you're saying is that it's been very lightly tested. :)

> regarding second architectures: when we started sending these patches
> around, there has been interest from some other architectures, so
> just because nobody else needs them now, it doesn't mean nobody will
> use them ever.

I was really interested in using them... until I looked at them.
Conceptually, they do something really useful, but the _implementation_
falls short of its promises.

I can't imagine ever using these hooks on x86.