linux-kernel - RE: [PATCH 2/2] thp: support split page table lock

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Date:	Fri,  6 Sep 2013 13:48:03 +0300 (EEST)
From:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc:	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Andi Kleen <andi@...stfloor.org>,
	Michal Hocko <mhocko@...e.cz>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	kirill.shutemov@...ux.intel.com,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Alex Thorlton <athorlton@....com>, linux-kernel@...r.kernel.org
Subject: RE: [PATCH 2/2] thp: support split page table lock

Naoya Horiguchi wrote:
> Thp related code also uses per process mm->page_table_lock now.
> So making it fine-grained can provide better performance.
> 
> This patch makes thp support split page table lock by using page->ptl
> of the pages storing "pmd_trans_huge" pmds.
> 
> Some functions like pmd_trans_huge_lock() and page_check_address_pmd()
> are expected by their caller to pass back the pointer of ptl, so this
> patch adds to those functions new arguments for that. Rather than that,
> this patch gives only straightforward replacement.
> 
> ChangeLog v3:
>  - fixed argument of huge_pmd_lockptr() in copy_huge_pmd()
>  - added missing declaration of ptl in do_huge_pmd_anonymous_page()
> 
> Signed-off-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>

Generally, looks good. Few notes:

I believe you need to convert __pte_alloc() to new locking. Not sure about
__pte_alloc_kernel().
Have you check all rest mm->page_table_lock, that they shouldn't be
converted to new locking?

You use uninitialized_var() a lot. It's ugly. I've check few places
(task_mmu.c, copy_huge_pmd) and have found a reason why we need it there.
Why?

You often do

+       ptl = huge_pmd_lockptr(mm, pmd);
+       spin_lock(ptl);

Should we have a helper to combine them? huge_pmd_lock()?

-- 
 Kirill A. Shutemov
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