linux-kernel - Re: [PATCH -mm v2] mm: add page_check_address

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Date:	Tue, 24 Nov 2015 12:36:17 +0300
From:	Vladimir Davydov <vdavydov@...tuozzo.com>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
CC:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -mm v2] mm: add page_check_address_transhuge helper

On Tue, Nov 24, 2015 at 11:09:30AM +0200, Kirill A. Shutemov wrote:
> On Tue, Nov 24, 2015 at 01:29:41PM +0900, Sergey Senozhatsky wrote:
...
> > mm/built-in.o: In function `page_referenced_one':
> > rmap.c:(.text+0x32070): undefined reference to `pmdp_clear_flush_young'
> 
> Something like this?
...
> @@ -929,9 +929,12 @@ static int page_referenced_one(struct page *page, struct vm_area_struct *vma,
>  				referenced++;
>  		}
>  		pte_unmap(pte);
> -	} else {
> +	} else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
>  		if (pmdp_clear_flush_young_notify(vma, address, pmd))
>  			referenced++;
> +	} else {
> +		/* unexpected pmd-mapped page? */
> +		WARN_ON_ONCE(1);
>  	}
>  	spin_unlock(ptl);

I think we'd better compile out page_check_address_transhuge altogether if
CONFIG_TRANSPARENT_HUGEPAGE is disabled and use page_check_address instead.
This would also reduce the kernel size a bit.
---
diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index b9eedc63e9e6..77d1ba57d495 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -219,9 +219,20 @@ static inline pte_t *page_check_address(struct page *page, struct mm_struct *mm,
  * Used by idle page tracking to check if a page was referenced via page
  * tables.
  */
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
 bool page_check_address_transhuge(struct page *page, struct mm_struct *mm,
 				  unsigned long address, pmd_t **pmdp,
 				  pte_t **ptep, spinlock_t **ptlp);
+#else
+static inline bool page_check_address_transhuge(struct page *page,
+				struct mm_struct *mm, unsigned long address,
+				pmd_t **pmdp, pte_t **ptep, spinlock_t **ptlp)
+{
+	*ptep = page_check_address(page, mm, address, ptlp, 0);
+	*pmdp = NULL;
+	return !!*ptep;
+}
+#endif
 
 /*
  * Used by swapoff to help locate where page is expected in vma.
diff --git a/mm/rmap.c b/mm/rmap.c
index 27916086ac50..6f371261dd12 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -798,6 +798,7 @@ int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma)
 	return 1;
 }
 
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
 /*
  * Check that @page is mapped at @address into @mm. In contrast to
  * page_check_address(), this function can handle transparent huge pages.
@@ -885,6 +886,7 @@ found:
 	*ptlp = ptl;
 	return true;
 }
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 
 struct page_referenced_arg {
 	int mapcount;
--
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