linux-kernel - Re: [RFC v5 3/3] mm: make swapin readahead to improve thp collapse rate

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Date:	Thu, 17 Sep 2015 16:28:25 +0300
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Ebru Akagunduz <ebru.akagunduz@...il.com>
Cc:	linux-mm@...ck.org, akpm@...ux-foundation.org,
	kirill.shutemov@...ux.intel.com, n-horiguchi@...jp.nec.com,
	aarcange@...hat.com, riel@...hat.com, iamjoonsoo.kim@....com,
	xiexiuqi@...wei.com, gorcunov@...nvz.org,
	linux-kernel@...r.kernel.org, mgorman@...e.de, rientjes@...gle.com,
	vbabka@...e.cz, aneesh.kumar@...ux.vnet.ibm.com, hughd@...gle.com,
	hannes@...xchg.org, mhocko@...e.cz, boaz@...xistor.com,
	raindel@...lanox.com
Subject: Re: [RFC v5 3/3] mm: make swapin readahead to improve thp collapse
 rate

On Mon, Sep 14, 2015 at 10:31:45PM +0300, Ebru Akagunduz wrote:
> @@ -2655,6 +2696,8 @@ static void collapse_huge_page(struct mm_struct *mm,
>  
>  	anon_vma_lock_write(vma->anon_vma);
>  
> +	__collapse_huge_page_swapin(mm, vma, address, pmd, pte);
> +

Do I miss something, or 'pte' is not initialized at this point?
And the value is not really used in __collapse_huge_page_swapin().

>  	pte = pte_offset_map(pmd, address);
>  	pte_ptl = pte_lockptr(mm, pmd);


>From 76783e1dfb22cde04cf46903336810df8a632617 Mon Sep 17 00:00:00 2001
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Date: Thu, 17 Sep 2015 16:23:30 +0300
Subject: [PATCH] khugepaged: __collapse_huge_page_swapin(): drop unused 'pte'
 parameter

'pte' dereference is eliminated by compiler, since nobody uses the
pteval until it's overwritten inside the loop.

Value of 'pte' itself is overwritten by pte_offset_map() before first
real use.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
---
 mm/huge_memory.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 4b057abd8615..5ad5c443cc94 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2628,11 +2628,10 @@ static bool hugepage_vma_check(struct vm_area_struct *vma)
 
 static void __collapse_huge_page_swapin(struct mm_struct *mm,
 					struct vm_area_struct *vma,
-					unsigned long address, pmd_t *pmd,
-					pte_t *pte)
+					unsigned long address, pmd_t *pmd)
 {
 	unsigned long _address;
-	pte_t pteval = *pte;
+	pte_t *pte, pteval;
 	int swapped_in = 0, ret = 0;
 
 	pte = pte_offset_map(pmd, address);
@@ -2730,7 +2729,7 @@ static void collapse_huge_page(struct mm_struct *mm,
 
 	anon_vma_lock_write(vma->anon_vma);
 
-	__collapse_huge_page_swapin(mm, vma, address, pmd, pte);
+	__collapse_huge_page_swapin(mm, vma, address, pmd);
 
 	pte = pte_offset_map(pmd, address);
 	pte_ptl = pte_lockptr(mm, pmd);
-- 
 Kirill A. Shutemov
--
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