[PATCH v2] mm/page_alloc: add a helper function to check page before alloc/free

The major portion of check_new_page() and free_pages_check() are same,
introduce a helper function check_one_page() for simplification.

Change in v2:
	- use bad_flags as parameter directly per Michal Hocko

Signed-off-by: Yaowei Bai <redacted>
---
 mm/page_alloc.c | 49 ++++++++++++++++++-------------------------------
 1 file changed, 18 insertions(+), 31 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 5b5240b..0a0acdb 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c

@@ -707,10 +707,9 @@ out:
 	zone->free_area[order].nr_free++;
 }
 
-static inline int free_pages_check(struct page *page)
+static inline int check_one_page(struct page *page, unsigned long bad_flags)
 {
 	const char *bad_reason = NULL;
-	unsigned long bad_flags = 0;
 
 	if (unlikely(page_mapcount(page)))
 		bad_reason = "nonzero mapcount";

@@ -718,9 +717,11 @@ static inline int free_pages_check(struct page *page)
 		bad_reason = "non-NULL mapping";
 	if (unlikely(atomic_read(&page->_count) != 0))
 		bad_reason = "nonzero _count";
-	if (unlikely(page->flags & PAGE_FLAGS_CHECK_AT_FREE)) {
-		bad_reason = "PAGE_FLAGS_CHECK_AT_FREE flag(s) set";
-		bad_flags = PAGE_FLAGS_CHECK_AT_FREE;
+	if (unlikely(page->flags & bad_flags)) {
+		if (bad_flags == PAGE_FLAGS_CHECK_AT_PREP)
+			bad_reason = "PAGE_FLAGS_CHECK_AT_PREP flag set";
+		else if (bad_flags == PAGE_FLAGS_CHECK_AT_FREE)
+			bad_reason = "PAGE_FLAGS_CHECK_AT_FREE flag set";
 	}
 #ifdef CONFIG_MEMCG
 	if (unlikely(page->mem_cgroup))

@@ -730,6 +731,17 @@ static inline int free_pages_check(struct page *page)
 		bad_page(page, bad_reason, bad_flags);
 		return 1;
 	}
+	return 0;
+}
+
+static inline int free_pages_check(struct page *page)
+{
+	int ret = 0;
+
+	ret = check_one_page(page, PAGE_FLAGS_CHECK_AT_FREE);
+	if (ret)
+		return ret;
+
 	page_cpupid_reset_last(page);
 	if (page->flags & PAGE_FLAGS_CHECK_AT_PREP)
 		page->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;

@@ -1287,32 +1299,7 @@ static inline void expand(struct zone *zone, struct page *page,
  */
 static inline int check_new_page(struct page *page)
 {
-	const char *bad_reason = NULL;
-	unsigned long bad_flags = 0;
-
-	if (unlikely(page_mapcount(page)))
-		bad_reason = "nonzero mapcount";
-	if (unlikely(page->mapping != NULL))
-		bad_reason = "non-NULL mapping";
-	if (unlikely(atomic_read(&page->_count) != 0))
-		bad_reason = "nonzero _count";
-	if (unlikely(page->flags & __PG_HWPOISON)) {
-		bad_reason = "HWPoisoned (hardware-corrupted)";
-		bad_flags = __PG_HWPOISON;
-	}
-	if (unlikely(page->flags & PAGE_FLAGS_CHECK_AT_PREP)) {
-		bad_reason = "PAGE_FLAGS_CHECK_AT_PREP flag set";
-		bad_flags = PAGE_FLAGS_CHECK_AT_PREP;
-	}
-#ifdef CONFIG_MEMCG
-	if (unlikely(page->mem_cgroup))
-		bad_reason = "page still charged to cgroup";
-#endif
-	if (unlikely(bad_reason)) {
-		bad_page(page, bad_reason, bad_flags);
-		return 1;
-	}
-	return 0;
+	return check_one_page(page, PAGE_FLAGS_CHECK_AT_PREP);
 }
 
 static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,

-- 
1.9.1


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On Tue 25-08-15 21:26:30, Yaowei Bai wrote:
[...]

 static inline int check_new_page(struct page *page)
 {
-	const char *bad_reason = NULL;
-	unsigned long bad_flags = 0;
-
-	if (unlikely(page_mapcount(page)))
-		bad_reason = "nonzero mapcount";
-	if (unlikely(page->mapping != NULL))
-		bad_reason = "non-NULL mapping";
-	if (unlikely(atomic_read(&page->_count) != 0))
-		bad_reason = "nonzero _count";
-	if (unlikely(page->flags & __PG_HWPOISON)) {
-		bad_reason = "HWPoisoned (hardware-corrupted)";
-		bad_flags = __PG_HWPOISON;
-	}

You have removed this check AFAICS. Now looking at 39ad4f19671d ("mm:
check __PG_HWPOISON separately from PAGE_FLAGS_CHECK_AT_*") I am not
sure it is correct to check it in the free path as it was removed from
the mask by this commit.

-	if (unlikely(page->flags & PAGE_FLAGS_CHECK_AT_PREP)) {
-		bad_reason = "PAGE_FLAGS_CHECK_AT_PREP flag set";
-		bad_flags = PAGE_FLAGS_CHECK_AT_PREP;
-	}
-#ifdef CONFIG_MEMCG
-	if (unlikely(page->mem_cgroup))
-		bad_reason = "page still charged to cgroup";
-#endif
-	if (unlikely(bad_reason)) {
-		bad_page(page, bad_reason, bad_flags);
-		return 1;
-	}
-	return 0;
+	return check_one_page(page, PAGE_FLAGS_CHECK_AT_PREP);
 }
 
 static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
-- 
1.9.1

-- 
Michal Hocko
SUSE Labs

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On Tue, Aug 25, 2015 at 04:03:22PM +0200, Michal Hocko wrote:

On Tue 25-08-15 21:26:30, Yaowei Bai wrote:
[...]

quoted

 static inline int check_new_page(struct page *page)
 {
-	const char *bad_reason = NULL;
-	unsigned long bad_flags = 0;
-
-	if (unlikely(page_mapcount(page)))
-		bad_reason = "nonzero mapcount";
-	if (unlikely(page->mapping != NULL))
-		bad_reason = "non-NULL mapping";
-	if (unlikely(atomic_read(&page->_count) != 0))
-		bad_reason = "nonzero _count";
-	if (unlikely(page->flags & __PG_HWPOISON)) {
-		bad_reason = "HWPoisoned (hardware-corrupted)";
-		bad_flags = __PG_HWPOISON;
-	}

You have removed this check AFAICS. Now looking at 39ad4f19671d ("mm:

I missed that check mistakenly, it should be there.

check __PG_HWPOISON separately from PAGE_FLAGS_CHECK_AT_*") I am not
sure it is correct to check it in the free path as it was removed from
the mask by this commit.

I investigated the commit you mentioned above. AFAICS, that commit assumes
that __PG_HWPOISON check should be performed in the alloc path, while in
the free path it doesn't need to. So there is a bit different in alloc/free
paths.
So Michal, do you think there is any obvious points to refactor these
two functions still? Anyway, appreciate your reviewing.

quoted

-	if (unlikely(page->flags & PAGE_FLAGS_CHECK_AT_PREP)) {
-		bad_reason = "PAGE_FLAGS_CHECK_AT_PREP flag set";
-		bad_flags = PAGE_FLAGS_CHECK_AT_PREP;
-	}
-#ifdef CONFIG_MEMCG
-	if (unlikely(page->mem_cgroup))
-		bad_reason = "page still charged to cgroup";
-#endif
-	if (unlikely(bad_reason)) {
-		bad_page(page, bad_reason, bad_flags);
-		return 1;
-	}
-	return 0;
+	return check_one_page(page, PAGE_FLAGS_CHECK_AT_PREP);
 }
 
 static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
-- 
1.9.1

-- 
Michal Hocko
SUSE Labs

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On Tue, Aug 25, 2015 at 04:03:22PM +0200, Michal Hocko wrote:

On Tue 25-08-15 21:26:30, Yaowei Bai wrote:
[...]

quoted

 static inline int check_new_page(struct page *page)
 {
-	const char *bad_reason = NULL;
-	unsigned long bad_flags = 0;
-
-	if (unlikely(page_mapcount(page)))
-		bad_reason = "nonzero mapcount";
-	if (unlikely(page->mapping != NULL))
-		bad_reason = "non-NULL mapping";
-	if (unlikely(atomic_read(&page->_count) != 0))
-		bad_reason = "nonzero _count";
-	if (unlikely(page->flags & __PG_HWPOISON)) {
-		bad_reason = "HWPoisoned (hardware-corrupted)";
-		bad_flags = __PG_HWPOISON;
-	}

You have removed this check AFAICS. Now looking at 39ad4f19671d ("mm:
check __PG_HWPOISON separately from PAGE_FLAGS_CHECK_AT_*") I am not
sure it is correct to check it in the free path as it was removed from
the mask by this commit.

I just refactored these two function and it looks well, will resend it soon.

quoted

-	if (unlikely(page->flags & PAGE_FLAGS_CHECK_AT_PREP)) {
-		bad_reason = "PAGE_FLAGS_CHECK_AT_PREP flag set";
-		bad_flags = PAGE_FLAGS_CHECK_AT_PREP;
-	}
-#ifdef CONFIG_MEMCG
-	if (unlikely(page->mem_cgroup))
-		bad_reason = "page still charged to cgroup";
-#endif
-	if (unlikely(bad_reason)) {
-		bad_page(page, bad_reason, bad_flags);
-		return 1;
-	}
-	return 0;
+	return check_one_page(page, PAGE_FLAGS_CHECK_AT_PREP);
 }
 
 static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
-- 
1.9.1

-- 
Michal Hocko
SUSE Labs

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