linux-kernel - Re: [PATCH] mm: use a irq-safe __mod_zone_page_state in mlocked_vma

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Date:	Sat, 10 May 2014 00:16:48 +0800
From:	Jianyu Zhan <nasa4836@...il.com>
To:	cl@...ux.com, akpm@...ux-foundation.org, mhocko@...e.cz,
	hannes@...xchg.org, riel@...hat.com, minchan@...nel.org,
	zhangyanfei@...fujitsu.com, hanpt@...ux.vnet.ibm.com,
	sasha.levin@...cle.com, oleg@...hat.com, fabf@...net.be,
	mgorman@...e.de, aarcange@...hat.com, cldu@...vell.com,
	nasa4836@...il.com
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: use a irq-safe __mod_zone_page_state in mlocked_vma_newpage()

>You are changing from the irq safe variant to __mod_zone_page_state which
>is *not* irq safe. Its legit to do so since presumably irqs are disabled
>anyways so you do not have to worry about irq safeness of
>__mod_zone_page_state.

>Please update the description. Its a bit confusing right now.

Hi, Christoph, I'm sorry for the misleading phrasing. 
Would be this one OK? Thanks.

--------<8---------
mm: use a light-weight __mod_zone_page_state in mlocked_vma_newpage()

mlocked_vma_newpage() is only called in fault path by
page_add_new_anon_rmap(), which is called on a *new* page.
And such page is initially only visible via the pagetables, and the
pte is locked while calling page_add_new_anon_rmap(), so we need not
use an irq-safe mod_zone_page_state() here, using a light-weight version
__mod_zone_page_state() would be OK.

Signed-off-by: Jianyu Zhan <nasa4836@...il.com>
---
 mm/internal.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/internal.h b/mm/internal.h
index 07b6736..69079b1 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -196,7 +196,7 @@ static inline int mlocked_vma_newpage(struct vm_area_struct *vma,
 		return 0;
 
 	if (!TestSetPageMlocked(page)) {
-		mod_zone_page_state(page_zone(page), NR_MLOCK,
+		__mod_zone_page_state(page_zone(page), NR_MLOCK,
 				    hpage_nr_pages(page));
 		count_vm_event(UNEVICTABLE_PGMLOCKED);
 	}
-- 
2.0.0-rc1

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