linux-kernel - Re: Handling NUMA page migration

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Date:	Wed, 5 Jun 2013 10:56:22 +0200
From:	Frank Mehnert <frank.mehnert@...cle.com>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	Robin Holt <holt@....com>, linux-mm@...ck.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Hugh Dickins <hughd@...gle.com>
Subject: Re: Handling NUMA page migration

On Wednesday 05 June 2013 10:34:13 Frank Mehnert wrote:
> On Wednesday 05 June 2013 09:54:54 Michal Hocko wrote:
> > On Tue 04-06-13 23:54:45, Frank Mehnert wrote:
> > > On Tuesday 04 June 2013 20:17:02 Frank Mehnert wrote:
> > > > On Tuesday 04 June 2013 16:02:30 Michal Hocko wrote:
> > > > > On Tue 04-06-13 14:14:45, Frank Mehnert wrote:
> > > > > > On Tuesday 04 June 2013 13:58:07 Robin Holt wrote:
> > > > > > > This is probably more appropriate to be directed at the
> > > > > > > linux-mm mailing list.
> > > > > > > 
> > > > > > > On Tue, Jun 04, 2013 at 09:22:10AM +0200, Frank Mehnert wrote:
> > > > > > > > Hi,
> > > > > > > > 
> > > > > > > > our memory management on Linux hosts conflicts with NUMA page
> > > > > > > > migration. I assume this problem existed for a longer time
> > > > > > > > but Linux 3.8 introduced automatic NUMA page balancing which
> > > > > > > > makes the problem visible on multi-node hosts leading to
> > > > > > > > kernel oopses.
> > > > > > > > 
> > > > > > > > NUMA page migration means that the physical address of a page
> > > > > > > > changes. This is fatal if the application assumes that this
> > > > > > > > never happens for that page as it was supposed to be pinned.
> > > > > > > > 
> > > > > > > > We have two kind of pinned memory:

Just to repeat it for reference:

A) 1. allocate memory in userland with mmap()
   2. madvise(MADV_DONTFORK)
   3. pin with get_user_pages().
   4. flush dcache_page()
   5. vm_flags |= (VM_DONTCOPY | VM_LOCKED)
      (resulting flags are VM_MIXEDMAP | VM_DONTDUMP | VM_DONTEXPAND |
       VM_DONTCOPY | VM_LOCKED | 0xff)

B) 1. allocate memory with alloc_pages()
   2. SetPageReserved()
   3. vm_mmap() to allocate a userspace mapping
   4. vm_insert_page()
   5. vm_flags |= (VM_DONTEXPAND | VM_DONTDUMP)
      (resulting flags are VM_MIXEDMAP | VM_DONTDUMP | VM_DONTEXPAND | 0xff)

The frequent case is B.

I've just disabled CONFIG_TRANSPARENT_HUGEPAGE for testing purposes and
the Oops is still triggered when running my testcase.

Thanks,

Frank
-- 
Dr.-Ing. Frank Mehnert | Software Development Director, VirtualBox
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