Date: Fri, 25 Mar 2011 10:45:24 -0500 (CDT)
From: Christoph Lameter <cl@linux.com>
To: Tejun Heo <tj@kernel.org>
cc: Eric Dumazet <eric.dumazet@gmail.com>, Pekka Enberg <penberg@kernel.org>,
        Ingo Molnar <mingo@elte.hu>, torvalds@linux-foundation.org,
        akpm@linux-foundation.org, npiggin@kernel.dk,
        David Rientjes <rientjes@google.com>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [GIT PULL] SLAB changes for v2.6.39-rc1
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On Fri, 25 Mar 2011, Tejun Heo wrote:

> I've looked through the code but can't figure out what the difference
> is.  The memset code is in mm/percpu-vm.c::pcpu_populate_chunk().
>
> 	for_each_possible_cpu(cpu)
> 		memset((void *)pcpu_chunk_addr(chunk, cpu, 0) + off, 0, size);
>
> (pcpu_chunk_addr(chunk, cpu, 0) + off) is the same vaddr as will be
> obtained by per_cpu_ptr(ptr, cpu), so all allocated memory regions are
> accessed before being returned.  Dazed and confused (seems like the
> theme of today for me).
>
> Could it be that the vmalloc page is taking more than one faults?

The vmalloc page only contains per cpu data from a single cpu right?

Could anyone have set write access restrictions that would require a fault
to get rid of?

Or does an access from a different cpu require a "page table sync"?

There is some rather strange looking code in arch/x86/mm/fault.c:vmalloc_fault


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