Re: [PATCH 11/11] mempolicy: apply page table walker on queue_pages_range()

From: Sasha Levin <sasha.levin@oracle.com>
To: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: linux-mm@kvack.org, akpm@linux-foundation.org, mpm@selenic.com,
	cpw@sgi.com, kosaki.motohiro@jp.fujitsu.com, hannes@cmpxchg.org,
	kamezawa.hiroyu@jp.fujitsu.com, mhocko@suse.cz,
	aneesh.kumar@linux.vnet.ibm.com, xemul@parallels.com,
	riel@redhat.com, kirill.shutemov@linux.intel.com,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 11/11] mempolicy: apply page table walker on queue_pages_range()
Date: Fri, 21 Feb 2014 12:18:11 -0500	[thread overview]
Message-ID: <53078A53.9030302@oracle.com> (raw)
In-Reply-To: <530785b2.d55c8c0a.3868.ffffa4e1SMTPIN_ADDED_BROKEN@mx.google.com>

On 02/21/2014 11:58 AM, Naoya Horiguchi wrote:
> Hi Sasha,
> 
> On Fri, Feb 21, 2014 at 01:30:53AM -0500, Sasha Levin wrote:
>> On 02/10/2014 04:44 PM, Naoya Horiguchi wrote:
>>> queue_pages_range() does page table walking in its own way now,
>>> so this patch rewrites it with walk_page_range().
>>> One difficulty was that queue_pages_range() needed to check vmas
>>> to determine whether we queue pages from a given vma or skip it.
>>> Now we have test_walk() callback in mm_walk for that purpose,
>>> so we can do the replacement cleanly. queue_pages_test_walk()
>>> depends on not only the current vma but also the previous one,
>>> so we use queue_pages->prev to keep it.
>>>
>>> ChangeLog v2:
>>> - rebase onto mmots
>>> - add VM_PFNMAP check on queue_pages_test_walk()
>>>
>>> Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
>>> ---
>>
>> Hi Naoya,
>>
>> I'm seeing another spew in today's -next, and it seems to be related
>> to this patch. Here's the spew (with line numbers instead of kernel
>> addresses):
> 
> Thanks. (line numbers translation is very helpful.)
> 
> This bug looks strange to me.
> "kernel BUG at mm/hugetlb.c:3580" means we try to do isolate_huge_page()
> for !PageHead page. But the caller queue_pages_hugetlb() gets the page
> with "page = pte_page(huge_ptep_get(pte))", so it should be the head page!
> 
> mm/hugetlb.c:3580 is VM_BUG_ON_PAGE(!PageHead(page), page), so we expect to
> have dump_page output at this point, is that in your kernel log?

This is usually a sign of a race between that code and thp splitting, see
https://lkml.org/lkml/2013/12/23/457 for example.

I forgot to add the dump_page output to my extraction process and the complete logs all long gone.
I'll grab it when it happens again.

Thanks,
Sasha

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