linux-kernel - Re: [PATCH v4 19/20] x86/mm: Add speculative pagefault handling

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Date:   Wed, 11 Oct 2017 11:39:58 +0200
From:   Laurent Dufour <ldufour@...ux.vnet.ibm.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     paulmck@...ux.vnet.ibm.com, peterz@...radead.org,
        kirill@...temov.name, ak@...ux.intel.com, mhocko@...nel.org,
        dave@...olabs.net, jack@...e.cz,
        Matthew Wilcox <willy@...radead.org>, benh@...nel.crashing.org,
        mpe@...erman.id.au, paulus@...ba.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, hpa@...or.com,
        Will Deacon <will.deacon@....com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        haren@...ux.vnet.ibm.com, khandual@...ux.vnet.ibm.com,
        npiggin@...il.com, bsingharora@...il.com,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        linuxppc-dev@...ts.ozlabs.org, x86@...nel.org
Subject: Re: [PATCH v4 19/20] x86/mm: Add speculative pagefault handling

On 10/10/2017 23:23, Andrew Morton wrote:
> On Mon,  9 Oct 2017 12:07:51 +0200 Laurent Dufour <ldufour@...ux.vnet.ibm.com> wrote:
> 
>> +/*
>> + * Advertise that we call the Speculative Page Fault handler.
>> + */
>> +#if defined(CONFIG_X86_64) && defined(CONFIG_SMP)
>> +#define __HAVE_ARCH_CALL_SPF
>> +#endif
> 
> Here's where I mess up your life ;)

That's ok... for this time ;)

> It would be more idiomatic to define this in arch/XXX/Kconfig:
> 
> config SPF
> 	def_bool y if SMP
> 
> then use CONFIG_SPF everywhere.

That's far smarter ! Thanks for the tip, I'll change the series in this way.

> Also, it would be better if CONFIG_SPF were defined at the start of the
> patch series rather than the end, so that as the patches add new code,
> that code is actually compilable.  For bisection purposes.  I can
> understand if this is too much work and effort - we can live with
> things the way they are now.

I'll make the change and define CONFIG_SPF earlier, since until the patch
enabling SPF page fault handler call in the arch part, the code is not
triggered but the sequence count and the RCU stuff will be called this way.


> This patchset is a ton of new code in very sensitive areas and seems to
> have received little review and test.  I can do a
> merge-and-see-what-happens but it would be quite a risk to send all
> this upstream based only on my sketchy review and linux-next runtime
> testing.  Can we bribe someone?

I'll do appreciate to get more review too. So please...