[PATCH V4 1/4] mm: set page->pfmemalloc in prep_new_page()

[Vlastimil Babka]

The function prep_new_page() sets almost everything in the struct page of the
page being allocated, except page->pfmemalloc. This is not obvious and has at
least once led to a bug where page->pfmemalloc was forgotten to be set
correctly, see commit 8fb74b9fb2b1 ("mm: compaction: partially revert capture
of suitable high-order page").

This patch moves the pfmemalloc setting to prep_new_page(), which means it
needs to gain alloc_flags parameter. The call to prep_new_page is moved from
buffered_rmqueue() to get_page_from_freelist(), which also leads to simpler
code. An obsolete comment for buffered_rmqueue() is replaced.

In addition to better maintainability there is a small reduction of code and
stack usage for get_page_from_freelist(), which inlines the other functions
involved.

add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-145 (-145)
function                                     old     new   delta
get_page_from_freelist                      2670    2525    -145

Stack usage is reduced from 184 to 168 bytes.

Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Zhang Yanfei <zhangyanfei@xxxxxxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxx>
---
 mm/page_alloc.c | 37 ++++++++++++++++---------------------
 1 file changed, 16 insertions(+), 21 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 1bb65e6..0c77a97 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -970,7 +970,8 @@ static inline int check_new_page(struct page *page)
 	return 0;
 }
 
-static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags)
+static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
+								int alloc_flags)
 {
 	int i;
 
@@ -994,6 +995,14 @@ static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags)
 
 	set_page_owner(page, order, gfp_flags);
 
+	/*
+	 * page->pfmemalloc is set when ALLOC_NO_WATERMARKS was necessary to
+	 * allocate the page. The expectation is that the caller is taking
+	 * steps that will free more memory. The caller should avoid the page
+	 * being used for !PFMEMALLOC purposes.
+	 */
+	page->pfmemalloc = !!(alloc_flags & ALLOC_NO_WATERMARKS);
+
 	return 0;
 }
 
@@ -1642,9 +1651,7 @@ int split_free_page(struct page *page)
 }
 
 /*
- * Really, prep_compound_page() should be called from __rmqueue_bulk().  But
- * we cheat by calling it from here, in the order > 0 path.  Saves a branch
- * or two.
+ * Allocate a page from the given zone. Use pcplists for order-0 allocations.
  */
 static inline
 struct page *buffered_rmqueue(struct zone *preferred_zone,
@@ -1655,7 +1662,6 @@ struct page *buffered_rmqueue(struct zone *preferred_zone,
 	struct page *page;
 	bool cold = ((gfp_flags & __GFP_COLD) != 0);
 
-again:
 	if (likely(order == 0)) {
 		struct per_cpu_pages *pcp;
 		struct list_head *list;
@@ -1711,8 +1717,6 @@ again:
 	local_irq_restore(flags);
 
 	VM_BUG_ON_PAGE(bad_range(zone, page), page);
-	if (prep_new_page(page, order, gfp_flags))
-		goto again;
 	return page;
 
 failed:
@@ -2177,25 +2181,16 @@ zonelist_scan:
 try_this_zone:
 		page = buffered_rmqueue(preferred_zone, zone, order,
 						gfp_mask, migratetype);
-		if (page)
-			break;
+		if (page) {
+			if (prep_new_page(page, order, gfp_mask, alloc_flags))
+				goto try_this_zone;
+			return page;
+		}
 this_zone_full:
 		if (IS_ENABLED(CONFIG_NUMA) && zlc_active)
 			zlc_mark_zone_full(zonelist, z);
 	}
 
-	if (page) {
-		/*
-		 * page->pfmemalloc is set when ALLOC_NO_WATERMARKS was
-		 * necessary to allocate the page. The expectation is
-		 * that the caller is taking steps that will free more
-		 * memory. The caller should avoid the page being used
-		 * for !PFMEMALLOC purposes.
-		 */
-		page->pfmemalloc = !!(alloc_flags & ALLOC_NO_WATERMARKS);
-		return page;
-	}
-
 	/*
 	 * The first pass makes sure allocations are spread fairly within the
 	 * local node.  However, the local node might have free pages left
-- 
2.1.2

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