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Date: Tue, 11 Mar 2014 01:07:52 -0400
From: Dave Jones <davej@redhat.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Linux Kernel <linux-kernel@vger.kernel.org>, linux-mm@kvack.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
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        Wanpeng Li <liwanp@linux.vnet.ibm.com>, Bob Liu <bob.liu@oracle.com>,
        Konstantin Khlebnikov <koct9i@gmail.com>
Subject: Re: bad rss-counter message in 3.14rc5
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On Mon, Mar 10, 2014 at 10:01:58PM -0700, Andrew Morton wrote:
 > On Tue, 11 Mar 2014 00:51:09 -0400 Dave Jones <davej@redhat.com> wrote:
 > 
 > > On Mon, Mar 10, 2014 at 09:46:12PM -0700, Andrew Morton wrote:
 > >  > On Mon, 10 Mar 2014 20:13:40 -0700 Andrew Morton <akpm@linux-foundation.org> wrote:
 > >  > 
 > >  > > > Anyone ? I'm hitting this trace on an almost daily basis, which is a pain
 > >  > > > while trying to reproduce a different bug..
 > >  > > 
 > >  > > Damn, I thought we'd fixed that but it seems not.  Cc's added.
 > >  > > 
 > >  > > Guys, what stops the migration target page from coming unlocked in
 > >  > > parallel with zap_pte_range()'s call to migration_entry_to_page()?
 > >  > 
 > >  > page_table_lock, sort-of.  At least, transitions of is_migration_entry()
 > >  > and page_locked() happen under ptl.
 > >  > 
 > >  > I don't see any holes in regular migration.  Do you know if this is
 > >  > reproducible with CONFIG_NUMA_BALANCING=n or CONFIG_NUMA=n?
 > > 
 > > CONFIG_NUMA_BALANCING was n already btw, so I'll do a NUMA=n run.
 > 
 > There probably isn't much point unless trinity is using
 > sys_move_pages().  Is it?

Trinity will do every syscall an arch has.

In the test case I have so far, I've narrowed it down to the vm group of syscalls
(so running with '-g vm' will do anything that I deemed 'vm'. Including.. sys_move_pages)
I'll try to narrow it down further tomorrow.

 >  If so it would be interesting to disable
 > trinity's move_pages calls and see if it still fails.
 
Ok, I'll try that first.

 > Grasping at straws here, trying to reduce the amount of code to look at :(

*nod*, it's not helped by the fact that the trace happens at process exit time
which could be considerably later after the syscall that buggers everything up
has happened.

	Dave