From: Peter Zijlstra <peterz@infradead.org>
To: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>,
Pankaj Gupta <pagupta@redhat.com>,
Tariq Toukan <ttoukan.linux@gmail.com>,
Mel Gorman <mgorman@techsingularity.net>,
Tariq Toukan <tariqt@mellanox.com>,
netdev@vger.kernel.org, akpm@linux-foundation.org,
linux-mm <linux-mm@kvack.org>,
Saeed Mahameed <saeedm@mellanox.com>,
linux-kernel@vger.kernel.org
Subject: Re: in_irq_or_nmi()
Date: Wed, 29 Mar 2017 11:19:49 +0200 [thread overview]
Message-ID: <20170329091949.o2kozhhdnszgwvtn@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20170329105928.609bc581@redhat.com>
On Wed, Mar 29, 2017 at 10:59:28AM +0200, Jesper Dangaard Brouer wrote:
> On Wed, 29 Mar 2017 10:12:19 +0200
> Peter Zijlstra <peterz@infradead.org> wrote:
>
> > On Mon, Mar 27, 2017 at 09:58:17AM -0700, Matthew Wilcox wrote:
> > > On Mon, Mar 27, 2017 at 05:15:00PM +0200, Jesper Dangaard Brouer wrote:
> > > > And I also verified it worked:
> > > >
> > > > 0.63 │ mov __preempt_count,%eax
> > > > │ free_hot_cold_page():
> > > > 1.25 │ test $0x1f0000,%eax
> > > > │ ↓ jne 1e4
> > > >
> > > > And this simplification also made the compiler change this into a
> > > > unlikely branch, which is a micro-optimization (that I will leave up to
> > > > the compiler).
> > >
> > > Excellent! That said, I think we should define in_irq_or_nmi() in
> > > preempt.h, rather than hiding it in the memory allocator. And since we're
> > > doing that, we might as well make it look like the other definitions:
> > >
> > > diff --git a/include/linux/preempt.h b/include/linux/preempt.h
> > > index 7eeceac52dea..af98c29abd9d 100644
> > > --- a/include/linux/preempt.h
> > > +++ b/include/linux/preempt.h
> > > @@ -81,6 +81,7 @@
> > > #define in_interrupt() (irq_count())
> > > #define in_serving_softirq() (softirq_count() & SOFTIRQ_OFFSET)
> > > #define in_nmi() (preempt_count() & NMI_MASK)
> > > +#define in_irq_or_nmi() (preempt_count() & (HARDIRQ_MASK | NMI_MASK))
> > > #define in_task() (!(preempt_count() & \
> > > (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET)))
> > >
> >
> > No, that's horrible. Also, wth is this about? A memory allocator that
> > needs in_nmi()? That sounds beyond broken.
>
> It is the other way around. We want to exclude NMI and HARDIRQ from
> using the per-cpu-pages (pcp) lists "order-0 cache" (they will
> fall-through using the normal buddy allocator path).
Any in_nmi() code arriving at the allocator is broken. No need to fix
the allocator.
next prev parent reply other threads:[~2017-03-29 9:20 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20170322234004.kffsce4owewgpqnm@techsingularity.net>
[not found] ` <20170323144347.1e6f29de@redhat.com>
[not found] ` <20170323145133.twzt4f5ci26vdyut@techsingularity.net>
[not found] ` <779ab72d-94b9-1a28-c192-377e91383b4e@gmail.com>
[not found] ` <1fc7338f-2b36-75f7-8a7e-8321f062207b@gmail.com>
[not found] ` <2123321554.7161128.1490599967015.JavaMail.zimbra@redhat.com>
[not found] ` <20170327105514.1ed5b1ba@redhat.com>
[not found] ` <20170327143947.4c237e54@redhat.com>
[not found] ` <20170327141518.GB27285@bombadil.infradead.org>
[not found] ` <20170327171500.4beef762@redhat.com>
2017-03-27 16:58 ` in_irq_or_nmi() Matthew Wilcox
2017-03-29 8:12 ` in_irq_or_nmi() Peter Zijlstra
2017-03-29 8:59 ` in_irq_or_nmi() Jesper Dangaard Brouer
2017-03-29 9:19 ` Peter Zijlstra [this message]
2017-03-29 18:12 ` in_irq_or_nmi() Matthew Wilcox
2017-03-29 19:11 ` in_irq_or_nmi() Jesper Dangaard Brouer
2017-03-29 19:44 ` in_irq_or_nmi() and RFC patch Jesper Dangaard Brouer
2017-03-30 6:49 ` Peter Zijlstra
2017-03-30 7:12 ` Jesper Dangaard Brouer
2017-03-30 7:35 ` Peter Zijlstra
2017-03-30 9:46 ` Jesper Dangaard Brouer
2017-03-30 13:04 ` Mel Gorman
2017-03-30 15:07 ` Jesper Dangaard Brouer
2017-04-03 12:05 ` Mel Gorman
2017-04-05 8:53 ` Mel Gorman
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