linux-kernel - Re: [PATCH 2/3] mm: use a light-weight __mod_zone_page_state in mlocked_vma

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Date:	Tue, 13 May 2014 01:58:01 +0800
From:	Jianyu Zhan <nasa4836@...il.com>
To:	akpm@...ux-foundation.org, mgorman@...e.de, nasa4836@...il.com,
	sasha.levin@...cle.com, zhangyanfei@...fujitsu.com,
	oleg@...hat.com, fabf@...net.be, cldu@...vell.com,
	iamjoonsoo.kim@....com, n-horiguchi@...jp.nec.com,
	kirill.shutemov@...ux.intel.com, schwidefsky@...ibm.com,
	gorcunov@...il.com
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] mm: use a light-weight __mod_zone_page_state in mlocked_vma_newpage() 

Andrew, since the previous patch

 [PATCH 1/3] mm: add comment for __mod_zone_page_stat

is updated, update this one accordingly.

-----<8-----
>From 9701fbdb3f9e7730b89780a5bf22effd1580cf35 Mon Sep 17 00:00:00 2001
From: Jianyu Zhan <nasa4836@...il.com>
Date: Tue, 13 May 2014 01:48:01 +0800
Subject: [PATCH] mm: fold mlocked_vma_newpage() into its only call site

In previous commit(mm: use the light version __mod_zone_page_state in
mlocked_vma_newpage()) a irq-unsafe __mod_zone_page_state is used.
And as suggested by Andrew, to reduce the risks that new call sites
incorrectly using mlocked_vma_newpage() without knowing they are adding
racing, this patch folds mlocked_vma_newpage() into its only call site,
page_add_new_anon_rmap, to make it open-cocded for people to know what
is going on.

Suggested-by: Andrew Morton <akpm@...ux-foundation.org>
Suggested-by: Hugh Dickins <hughd@...gle.com>
Signed-off-by: Jianyu Zhan <nasa4836@...il.com>
---
 mm/internal.h | 29 -----------------------------
 mm/rmap.c     | 20 +++++++++++++++++---
 2 files changed, 17 insertions(+), 32 deletions(-)

diff --git a/mm/internal.h b/mm/internal.h
index d6a4868..29f3dc8 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -184,31 +184,6 @@ static inline void munlock_vma_pages_all(struct vm_area_struct *vma)
 }
 
 /*
- * Called only in fault path, to determine if a new page is being
- * mapped into a LOCKED vma.  If it is, mark page as mlocked.
- */
-static inline int mlocked_vma_newpage(struct vm_area_struct *vma,
-				    struct page *page)
-{
-	VM_BUG_ON_PAGE(PageLRU(page), page);
-
-	if (likely((vma->vm_flags & (VM_LOCKED | VM_SPECIAL)) != VM_LOCKED))
-		return 0;
-
-	if (!TestSetPageMlocked(page)) {
-		/*
-		 * We use the irq-unsafe __mod_zone_page_stat because
-		 * this counter is not modified from interrupt context, and the
-		 * pte lock is held(spinlock), which implies preemption disabled.
-		 */
-		__mod_zone_page_state(page_zone(page), NR_MLOCK,
-				    hpage_nr_pages(page));
-		count_vm_event(UNEVICTABLE_PGMLOCKED);
-	}
-	return 1;
-}
-
-/*
  * must be called with vma's mmap_sem held for read or write, and page locked.
  */
 extern void mlock_vma_page(struct page *page);
@@ -250,10 +225,6 @@ extern unsigned long vma_address(struct page *page,
 				 struct vm_area_struct *vma);
 #endif
 #else /* !CONFIG_MMU */
-static inline int mlocked_vma_newpage(struct vm_area_struct *v, struct page *p)
-{
-	return 0;
-}
 static inline void clear_page_mlock(struct page *page) { }
 static inline void mlock_vma_page(struct page *page) { }
 static inline void mlock_migrate_page(struct page *new, struct page *old) { }
diff --git a/mm/rmap.c b/mm/rmap.c
index fa73194..386b78f 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1029,11 +1029,25 @@ void page_add_new_anon_rmap(struct page *page,
 	__mod_zone_page_state(page_zone(page), NR_ANON_PAGES,
 			hpage_nr_pages(page));
 	__page_set_anon_rmap(page, vma, address, 1);
-	if (!mlocked_vma_newpage(vma, page)) {
+
+	VM_BUG_ON_PAGE(PageLRU(page), page);
+	if (likely((vma->vm_flags & (VM_LOCKED | VM_SPECIAL)) != VM_LOCKED)) {
 		SetPageActive(page);
 		lru_cache_add(page);
-	} else
-		add_page_to_unevictable_list(page);
+		return;
+	}
+
+	if (!TestSetPageMlocked(page)) {
+		/*
+		 * We use the irq-unsafe __mod_zone_page_stat because
+		 * this counter is not modified from interrupt context, and the
+		 * pte lock is held(spinlock), which implies preemption disabled.
+		 */
+		__mod_zone_page_state(page_zone(page), NR_MLOCK,
+				    hpage_nr_pages(page));
+		count_vm_event(UNEVICTABLE_PGMLOCKED);
+	}
+	add_page_to_unevictable_list(page);
 }
 
 /**
-- 
2.0.0-rc1

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