linux-kernel - Re: hugepage related lockdep trace.

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Message-ID: <87d2qfck2l.fsf@linux.vnet.ibm.com>
Date:	Fri, 19 Jul 2013 08:50:02 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Hillf Danton <dhillf@...il.com>
Cc:	Minchan Kim <minchan@...nel.org>, Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	linux-mm@...ck.org, Rik van Riel <riel@...hat.com>,
	Michal Hocko <mhocko@...e.cz>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: hugepage related lockdep trace.

Hillf Danton <dhillf@...il.com> writes:

> On Fri, Jul 19, 2013 at 1:42 AM, Aneesh Kumar K.V
> <aneesh.kumar@...ux.vnet.ibm.com> wrote:
>> Minchan Kim <minchan@...nel.org> writes:
>>> IMHO, it's a false positive because i_mmap_mutex was held by kswapd
>>> while one in the middle of fault path could be never on kswapd context.
>>>
>>> It seems lockdep for reclaim-over-fs isn't enough smart to identify
>>> between background and direct reclaim.
>>>
>>> Wait for other's opinion.
>>
>> Is that reasoning correct ?. We may not deadlock because hugetlb pages
>> cannot be reclaimed. So the fault path in hugetlb won't end up
>> reclaiming pages from same inode. But the report is correct right ?
>>
>>
>> Looking at the hugetlb code we have in huge_pmd_share
>>
>> out:
>>         pte = (pte_t *)pmd_alloc(mm, pud, addr);
>>         mutex_unlock(&mapping->i_mmap_mutex);
>>         return pte;
>>
>> I guess we should move that pmd_alloc outside i_mmap_mutex. Otherwise
>> that pmd_alloc can result in a reclaim which can call shrink_page_list ?
>>
> Hm, can huge pages be reclaimed, say by kswapd currently?

No we don't reclaim hugetlb pages.

-aneesh

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