From: Peter Zijlstra <peterz@infradead.org>
To: Vineet Gupta <Vineet.Gupta1@synopsys.com>
Cc: Nicolas Pitre <nicolas.pitre@linaro.org>,
Andrew Morton <akpm@linux-foundation.org>,
David Hildenbrand <dahi@linux.vnet.ibm.com>,
Thomas Petazzoni <thomas.petazzoni@free-electrons.com>,
Russell King <linux@arm.linux.org.uk>,
lkml <linux-kernel@vger.kernel.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>
Subject: Re: kmap_atomic and preemption
Date: Wed, 4 May 2016 17:01:38 +0200 [thread overview]
Message-ID: <20160504150138.GR3430@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <C2D7FE5348E1B147BCA15975FBA23075F4EA065E@us01wembx1.internal.synopsys.com>
On Wed, May 04, 2016 at 02:16:11PM +0000, Vineet Gupta wrote:
> > static inline void *kmap_atomic(struct page *page)
> > {
> > preempt_disable();
> > pagefault_disable();
> > if (!PageHighMem(page))
> > return page_address(page);
> >
> > return __kmap_atomic(page);
> > }
>
> I actually want to return early for !PageHighMem and avoid the pointless 2
> LD-ADD-ST to memory for map and 2 LD-SUB-ST for unmap for regular pages for such
> cases.
So I'm fairly sure people rely on the fact you cannot have pagefault
inside a kmap_atomic().
But you could potentially get away with leaving preemption enabled. Give
it a try, see if something goes *bang* ;-)
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WARNING: multiple messages have this Message-ID (diff)
From: Peter Zijlstra <peterz@infradead.org>
To: Vineet Gupta <Vineet.Gupta1@synopsys.com>
Cc: Nicolas Pitre <nicolas.pitre@linaro.org>,
Andrew Morton <akpm@linux-foundation.org>,
David Hildenbrand <dahi@linux.vnet.ibm.com>,
Thomas Petazzoni <thomas.petazzoni@free-electrons.com>,
Russell King <linux@arm.linux.org.uk>,
lkml <linux-kernel@vger.kernel.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>
Subject: Re: kmap_atomic and preemption
Date: Wed, 4 May 2016 17:01:38 +0200 [thread overview]
Message-ID: <20160504150138.GR3430@twins.programming.kicks-ass.net> (raw)
Message-ID: <20160504150138.6OZAbLtxLNqLdA0t32ftFI2RV0x3kt13kwSyXOD09LQ@z> (raw)
In-Reply-To: <C2D7FE5348E1B147BCA15975FBA23075F4EA065E@us01wembx1.internal.synopsys.com>
On Wed, May 04, 2016 at 02:16:11PM +0000, Vineet Gupta wrote:
> > static inline void *kmap_atomic(struct page *page)
> > {
> > preempt_disable();
> > pagefault_disable();
> > if (!PageHighMem(page))
> > return page_address(page);
> >
> > return __kmap_atomic(page);
> > }
>
> I actually want to return early for !PageHighMem and avoid the pointless 2
> LD-ADD-ST to memory for map and 2 LD-SUB-ST for unmap for regular pages for such
> cases.
So I'm fairly sure people rely on the fact you cannot have pagefault
inside a kmap_atomic().
But you could potentially get away with leaving preemption enabled. Give
it a try, see if something goes *bang* ;-)
next prev parent reply other threads:[~2016-05-04 15:01 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-04 10:37 kmap_atomic and preemption Vineet Gupta
2016-05-04 10:37 ` Vineet Gupta
2016-05-04 13:47 ` Peter Zijlstra
2016-05-04 13:47 ` Peter Zijlstra
2016-05-04 13:53 ` Thomas Petazzoni
2016-05-04 13:53 ` Thomas Petazzoni
2016-05-04 14:01 ` Vineet Gupta
2016-05-04 14:01 ` Vineet Gupta
2016-05-04 14:16 ` Vineet Gupta
2016-05-04 14:16 ` Vineet Gupta
2016-05-04 15:01 ` Peter Zijlstra [this message]
2016-05-04 15:01 ` Peter Zijlstra
2016-05-05 12:37 ` Vineet Gupta
2016-05-05 12:37 ` Vineet Gupta
2016-05-04 19:17 ` Russell King - ARM Linux
2016-05-04 19:17 ` Russell King - ARM Linux
2016-05-05 9:37 ` Peter Zijlstra
2016-05-05 9:37 ` Peter Zijlstra
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