linux-kernel - Re: [PATCHv5 01/28] mm, proc: adjust PSS calculation

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Date:	Fri, 15 May 2015 13:33:31 +0200
From:	Vlastimil Babka <vbabka@...e.cz>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
CC:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Hugh Dickins <hughd@...gle.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Christoph Lameter <cl@...two.org>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Steve Capper <steve.capper@...aro.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	Jerome Marchand <jmarchan@...hat.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCHv5 01/28] mm, proc: adjust PSS calculation

On 05/15/2015 12:56 PM, Kirill A. Shutemov wrote:
> On Thu, May 14, 2015 at 04:12:29PM +0200, Vlastimil Babka wrote:
>> On 04/23/2015 11:03 PM, Kirill A. Shutemov wrote:
>>> With new refcounting all subpages of the compound page are not nessessary
>>> have the same mapcount. We need to take into account mapcount of every
>>> sub-page.
>>>
>>> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
>>> Tested-by: Sasha Levin <sasha.levin@...cle.com>
>>
>> Acked-by: Vlastimil Babka <vbabka@...e.cz>
>>
>> (some nitpicks below)
>>
>>> ---
>>>   fs/proc/task_mmu.c | 43 ++++++++++++++++++++++---------------------
>>>   1 file changed, 22 insertions(+), 21 deletions(-)
>>>
>>> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
>>> index 956b75d61809..95bc384ee3f7 100644
>>> --- a/fs/proc/task_mmu.c
>>> +++ b/fs/proc/task_mmu.c
>>> @@ -449,9 +449,10 @@ struct mem_size_stats {
>>>   };
>>>
>>>   static void smaps_account(struct mem_size_stats *mss, struct page *page,
>>> -		unsigned long size, bool young, bool dirty)
>>> +		bool compound, bool young, bool dirty)
>>>   {
>>> -	int mapcount;
>>> +	int i, nr = compound ? hpage_nr_pages(page) : 1;
>>
>> Why not just HPAGE_PMD_NR instead of hpage_nr_pages(page)?
>
> Okay, makes sense. Compiler is smart enough to optimize away HPAGE_PMD_NR
> for THP=n. (HPAGE_PMD_NR is BUILD_BUG() for THP=n)

Ah, BUILD_BUG()... I'm not sure we can rely on optimization to avoid 
BUILD_BUG(), what if somebody compiles with all optimizations off?
So why not replace BUILD_BUG() with "1", or create a variant of 
HPAGE_PMD_NR that does that, for this case and patch 3. Seems better 
than testing PageTransHuge everywhere...
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