mm/page_alloc: split out buddy removal code from rmqueue into separate helper

This is a preparation page to allow the buddy removal code to be reused in
a later patch.

No functional change.

Link: https://lkml.kernel.org/r/20220624125423.6126-4-mgorman@techsingularity.netSigned-off-by: NMel Gorman <mgorman@techsingularity.net>
Tested-by: NMinchan Kim <minchan@kernel.org>
Acked-by: NMinchan Kim <minchan@kernel.org>
Reviewed-by: NNicolas Saenz Julienne <nsaenzju@redhat.com>
Acked-by: NVlastimil Babka <vbabka@suse.cz>
Tested-by: NYu Zhao <yuzhao@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>

mm/page_alloc.c

@@ -3641,6 +3641,43 @@ static inline void zone_statistics(struct zone *preferred_zone, struct zone *z,
 #endif
 }
 
+static __always_inline
+struct page *rmqueue_buddy(struct zone *preferred_zone, struct zone *zone,
+			   unsigned int order, unsigned int alloc_flags,
+			   int migratetype)
+{
+	struct page *page;
+	unsigned long flags;
+
+	do {
+		page = NULL;
+		spin_lock_irqsave(&zone->lock, flags);
+		/*
+		 * order-0 request can reach here when the pcplist is skipped
+		 * due to non-CMA allocation context. HIGHATOMIC area is
+		 * reserved for high-order atomic allocation, so order-0
+		 * request should skip it.
+		 */
+		if (order > 0 && alloc_flags & ALLOC_HARDER)
+			page = __rmqueue_smallest(zone, order, MIGRATE_HIGHATOMIC);
+		if (!page) {
+			page = __rmqueue(zone, order, migratetype, alloc_flags);
+			if (!page) {
+				spin_unlock_irqrestore(&zone->lock, flags);
+				return NULL;
+			}
+		}
+		__mod_zone_freepage_state(zone, -(1 << order),
+					  get_pcppage_migratetype(page));
+		spin_unlock_irqrestore(&zone->lock, flags);
+	} while (check_new_pages(page, order));
+
+	__count_zid_vm_events(PGALLOC, page_zonenum(page), 1 << order);
+	zone_statistics(preferred_zone, zone, 1);
+
+	return page;
+}
+
 /* Remove page from the per-cpu list, caller must protect the list */
 static inline
 struct page *__rmqueue_pcplist(struct zone *zone, unsigned int order,
@@ -3721,9 +3758,14 @@ struct page *rmqueue(struct zone *preferred_zone,
 			gfp_t gfp_flags, unsigned int alloc_flags,
 			int migratetype)
 {
-	unsigned long flags;
 	struct page *page;
 
+	/*
+	 * We most definitely don't want callers attempting to
+	 * allocate greater than order-1 page units with __GFP_NOFAIL.
+	 */
+	WARN_ON_ONCE((gfp_flags & __GFP_NOFAIL) && (order > 1));
+
 	if (likely(pcp_allowed_order(order))) {
 		/*
 		 * MIGRATE_MOVABLE pcplist could have the pages on CMA area and
@@ -3737,35 +3779,10 @@ struct page *rmqueue(struct zone *preferred_zone,
 		}
 	}
 
-	/*
-	 * We most definitely don't want callers attempting to
-	 * allocate greater than order-1 page units with __GFP_NOFAIL.
-	 */
-	WARN_ON_ONCE((gfp_flags & __GFP_NOFAIL) && (order > 1));
-
-	do {
-		page = NULL;
-		spin_lock_irqsave(&zone->lock, flags);
-		/*
-		 * order-0 request can reach here when the pcplist is skipped
-		 * due to non-CMA allocation context. HIGHATOMIC area is
-		 * reserved for high-order atomic allocation, so order-0
-		 * request should skip it.
-		 */
-		if (order > 0 && alloc_flags & ALLOC_HARDER)
-			page = __rmqueue_smallest(zone, order, MIGRATE_HIGHATOMIC);
-		if (!page) {
-			page = __rmqueue(zone, order, migratetype, alloc_flags);
-			if (!page)
-				goto failed;
-		}
-		__mod_zone_freepage_state(zone, -(1 << order),
-					  get_pcppage_migratetype(page));
-		spin_unlock_irqrestore(&zone->lock, flags);
-	} while (check_new_pages(page, order));
-
-	__count_zid_vm_events(PGALLOC, page_zonenum(page), 1 << order);
-	zone_statistics(preferred_zone, zone, 1);
+	page = rmqueue_buddy(preferred_zone, zone, order, alloc_flags,
+							migratetype);
+	if (unlikely(!page))
+		return NULL;
 
 out:
 	/* Separate test+clear to avoid unnecessary atomics */
@@ -3776,10 +3793,6 @@ struct page *rmqueue(struct zone *preferred_zone,
 
 	VM_BUG_ON_PAGE(page && bad_range(zone, page), page);
 	return page;
-
-failed:
-	spin_unlock_irqrestore(&zone->lock, flags);
-	return NULL;
 }
 
 #ifdef CONFIG_FAIL_PAGE_ALLOC