linux-kernel - Re: [PATCH 3/4] kernel.h: Add non_block

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Date:   Fri, 23 Aug 2019 09:12:34 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Daniel Vetter <daniel@...ll.ch>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Intel Graphics Development <intel-gfx@...ts.freedesktop.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Michal Hocko <mhocko@...e.com>,
        David Rientjes <rientjes@...gle.com>,
        Christian König <christian.koenig@....com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Wei Wang <wvw@...gle.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jann Horn <jannh@...gle.com>, Feng Tang <feng.tang@...el.com>,
        Kees Cook <keescook@...omium.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Daniel Vetter <daniel.vetter@...el.com>
Subject: Re: [PATCH 3/4] kernel.h: Add non_block_start/end()

On Fri, Aug 23, 2019 at 10:34:01AM +0200, Daniel Vetter wrote:
> On Fri, Aug 23, 2019 at 1:14 AM Andrew Morton <akpm@...ux-foundation.org> wrote:
> >
> > On Tue, 20 Aug 2019 22:24:40 +0200 Daniel Vetter <daniel@...ll.ch> wrote:
> >
> > > Hi Peter,
> > >
> > > Iirc you've been involved at least somewhat in discussing this. -mm folks
> > > are a bit undecided whether these new non_block semantics are a good idea.
> > > Michal Hocko still is in support, but Andrew Morton and Jason Gunthorpe
> > > are less enthusiastic. Jason said he's ok with merging the hmm side of
> > > this if scheduler folks ack. If not, then I'll respin with the
> > > preempt_disable/enable instead like in v1.
> >
> > I became mollified once Michel explained the rationale.  I think it's
> > OK.  It's very specific to the oom reaper and hopefully won't be used
> > more widely(?).
> 
> Yeah, no plans for that from me. And I hope the comment above them now
> explains why they exist, so people think twice before using it in
> random places.

I still haven't heard a satisfactory answer why a whole new scheme is
needed and a simple:

   if (IS_ENABLED(CONFIG_DEBUG_ATOMIC_SLEEP))
        preempt_disable()

isn't sufficient to catch the problematic cases during debugging??
IMHO the fact preempt is changed by the above when debugging is not
material here. I think that information should be included in the
commit message at least.

But if sched people are happy then lets go ahead. Can you send a v2
with the check encompassing the invalidate_range_end?

Jason