From: Vlastimil Babka <vbabka@suse.cz>
To: Andrew Morton <akpm@linux-foundation.org>,
"Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Christoph Lameter <cl@linux.com>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Hugh Dickins <hughd@google.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Dave Hansen <dave.hansen@intel.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Michal Hocko <mhocko@suse.cz>,
David Rientjes <rientjes@google.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCHv3 4/5] mm: make compound_head() robust
Date: Mon, 24 Aug 2015 17:49:45 +0200 [thread overview]
Message-ID: <55DB3D19.8070009@suse.cz> (raw)
In-Reply-To: <20150821123458.b3a6947135d5b506a34abc61@linux-foundation.org>
On 08/21/2015 09:34 PM, Andrew Morton wrote:
> On Fri, 21 Aug 2015 22:31:09 +0300 "Kirill A. Shutemov" <kirill@shutemov.name> wrote:
>
>> On Fri, Aug 21, 2015 at 11:11:27AM -0500, Christoph Lameter wrote:
>>> On Fri, 21 Aug 2015, Kirill A. Shutemov wrote:
>>>
>>>>> Is this really true? For example if it's a slab page, will that page
>>>>> ever be inspected by code which is looking for the PageTail bit?
>>>>
>>>> +Christoph.
>>>>
>>>> What we know for sure is that space is not used in tail pages, otherwise
>>>> it would collide with current compound_dtor.
>>>
>>> Sl*b allocators only do a virt_to_head_page on tail pages.
>>
>> The question was whether it's safe to assume that the bit 0 is always zero
>> in the word as this bit will encode PageTail().
>
> That wasn't my question actually...
>
> What I'm wondering is: if this page is being used for slab, will any
> code path ever run PageTail() against it? If not, we don't need to be
> concerned about that bit.
Pfn scanners such as compaction might inspect such pages and run
compound_head() (and thus PageTail) on them. I think no kind of page
within a zone (slab or otherwise) is "protected" from this, which is why
it needs to be robust.
> And slab was just the example I chose. The same question petains to
> all other uses of that union.
>
WARNING: multiple messages have this Message-ID (diff)
From: Vlastimil Babka <vbabka@suse.cz>
To: Andrew Morton <akpm@linux-foundation.org>,
"Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Christoph Lameter <cl@linux.com>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Hugh Dickins <hughd@google.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Dave Hansen <dave.hansen@intel.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Michal Hocko <mhocko@suse.cz>,
David Rientjes <rientjes@google.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCHv3 4/5] mm: make compound_head() robust
Date: Mon, 24 Aug 2015 17:49:45 +0200 [thread overview]
Message-ID: <55DB3D19.8070009@suse.cz> (raw)
In-Reply-To: <20150821123458.b3a6947135d5b506a34abc61@linux-foundation.org>
On 08/21/2015 09:34 PM, Andrew Morton wrote:
> On Fri, 21 Aug 2015 22:31:09 +0300 "Kirill A. Shutemov" <kirill@shutemov.name> wrote:
>
>> On Fri, Aug 21, 2015 at 11:11:27AM -0500, Christoph Lameter wrote:
>>> On Fri, 21 Aug 2015, Kirill A. Shutemov wrote:
>>>
>>>>> Is this really true? For example if it's a slab page, will that page
>>>>> ever be inspected by code which is looking for the PageTail bit?
>>>>
>>>> +Christoph.
>>>>
>>>> What we know for sure is that space is not used in tail pages, otherwise
>>>> it would collide with current compound_dtor.
>>>
>>> Sl*b allocators only do a virt_to_head_page on tail pages.
>>
>> The question was whether it's safe to assume that the bit 0 is always zero
>> in the word as this bit will encode PageTail().
>
> That wasn't my question actually...
>
> What I'm wondering is: if this page is being used for slab, will any
> code path ever run PageTail() against it? If not, we don't need to be
> concerned about that bit.
Pfn scanners such as compaction might inspect such pages and run
compound_head() (and thus PageTail) on them. I think no kind of page
within a zone (slab or otherwise) is "protected" from this, which is why
it needs to be robust.
> And slab was just the example I chose. The same question petains to
> all other uses of that union.
>
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next prev parent reply other threads:[~2015-08-24 15:49 UTC|newest]
Thread overview: 96+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-08-19 9:21 [PATCHv3 0/5] Fix compound_head() race Kirill A. Shutemov
2015-08-19 9:21 ` Kirill A. Shutemov
2015-08-19 9:21 ` [PATCHv3 1/5] mm: drop page->slab_page Kirill A. Shutemov
2015-08-19 9:21 ` Kirill A. Shutemov
2015-08-24 14:59 ` Vlastimil Babka
2015-08-24 14:59 ` Vlastimil Babka
2015-08-24 15:02 ` Vlastimil Babka
2015-08-24 15:02 ` Vlastimil Babka
2015-08-25 17:24 ` Kirill A. Shutemov
2015-08-25 17:24 ` Kirill A. Shutemov
2015-08-19 9:21 ` [PATCHv3 2/5] zsmalloc: use page->private instead of page->first_page Kirill A. Shutemov
2015-08-19 9:21 ` Kirill A. Shutemov
2015-08-24 15:04 ` Vlastimil Babka
2015-08-24 15:04 ` Vlastimil Babka
2015-08-19 9:21 ` [PATCHv3 3/5] mm: pack compound_dtor and compound_order into one word in struct page Kirill A. Shutemov
2015-08-19 9:21 ` Kirill A. Shutemov
2015-08-20 23:26 ` Andrew Morton
2015-08-20 23:26 ` Andrew Morton
2015-08-21 7:13 ` Michal Hocko
2015-08-21 7:13 ` Michal Hocko
2015-08-21 10:40 ` Kirill A. Shutemov
2015-08-21 10:40 ` Kirill A. Shutemov
2015-08-21 10:51 ` Michal Hocko
2015-08-21 10:51 ` Michal Hocko
2015-08-19 9:21 ` [PATCHv3 4/5] mm: make compound_head() robust Kirill A. Shutemov
2015-08-19 9:21 ` Kirill A. Shutemov
2015-08-20 23:36 ` Andrew Morton
2015-08-20 23:36 ` Andrew Morton
2015-08-21 12:10 ` Kirill A. Shutemov
2015-08-21 12:10 ` Kirill A. Shutemov
2015-08-21 16:11 ` Christoph Lameter
2015-08-21 16:11 ` Christoph Lameter
2015-08-21 19:31 ` Kirill A. Shutemov
2015-08-21 19:31 ` Kirill A. Shutemov
2015-08-21 19:34 ` Andrew Morton
2015-08-21 19:34 ` Andrew Morton
2015-08-21 21:15 ` Christoph Lameter
2015-08-21 21:15 ` Christoph Lameter
2015-08-24 15:49 ` Vlastimil Babka [this message]
2015-08-24 15:49 ` Vlastimil Babka
2015-08-25 11:44 ` Vlastimil Babka
2015-08-25 11:44 ` Vlastimil Babka
2015-08-25 18:33 ` Kirill A. Shutemov
2015-08-25 18:33 ` Kirill A. Shutemov
2015-08-25 20:11 ` Paul E. McKenney
2015-08-25 20:11 ` Paul E. McKenney
2015-08-25 20:46 ` Vlastimil Babka
2015-08-25 20:46 ` Vlastimil Babka
2015-08-25 21:19 ` Paul E. McKenney
2015-08-25 21:19 ` Paul E. McKenney
2015-08-26 15:04 ` Kirill A. Shutemov
2015-08-26 15:04 ` Kirill A. Shutemov
2015-08-26 15:39 ` Vlastimil Babka
2015-08-26 15:39 ` Vlastimil Babka
2015-08-26 16:38 ` Paul E. McKenney
2015-08-26 16:38 ` Paul E. McKenney
2015-08-26 18:18 ` Hugh Dickins
2015-08-26 18:18 ` Hugh Dickins
2015-08-26 21:29 ` Paul E. McKenney
2015-08-26 21:29 ` Paul E. McKenney
2015-08-26 22:28 ` Hugh Dickins
2015-08-26 22:28 ` Hugh Dickins
2015-08-26 23:34 ` Paul E. McKenney
2015-08-26 23:34 ` Paul E. McKenney
2015-08-27 15:09 ` Michal Hocko
2015-08-27 15:09 ` Michal Hocko
2015-08-27 16:03 ` Michal Hocko
2015-08-27 16:03 ` Michal Hocko
2015-08-27 17:28 ` Hugh Dickins
2015-08-27 17:28 ` Hugh Dickins
2015-08-27 18:06 ` Michal Hocko
2015-08-27 18:06 ` Michal Hocko
2015-08-27 16:36 ` Paul E. McKenney
2015-08-27 16:36 ` Paul E. McKenney
2015-08-27 18:14 ` Michal Hocko
2015-08-27 18:14 ` Michal Hocko
2015-08-27 19:01 ` Paul E. McKenney
2015-08-27 19:01 ` Paul E. McKenney
2015-08-23 23:59 ` Jesper Dangaard Brouer
2015-08-23 23:59 ` Jesper Dangaard Brouer
2015-08-24 9:29 ` Kirill A. Shutemov
2015-08-24 9:29 ` Kirill A. Shutemov
2015-08-24 10:17 ` Kirill A. Shutemov
2015-08-24 10:17 ` Kirill A. Shutemov
2015-08-19 9:21 ` [PATCHv3 5/5] mm: use 'unsigned int' for page order Kirill A. Shutemov
2015-08-19 9:21 ` Kirill A. Shutemov
2015-08-20 8:32 ` Michal Hocko
2015-08-20 8:32 ` Michal Hocko
2015-08-20 12:31 ` [PATCHv3 0/5] Fix compound_head() race Kirill A. Shutemov
2015-08-20 12:31 ` Kirill A. Shutemov
2015-08-20 23:38 ` Andrew Morton
2015-08-20 23:38 ` Andrew Morton
2015-08-22 20:13 ` Hugh Dickins
2015-08-22 20:13 ` Hugh Dickins
2015-08-24 9:36 ` Kirill A. Shutemov
2015-08-24 9:36 ` Kirill A. Shutemov
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