mm/page_owner: don't define fields on struct page_ext by hard-coding

There is a memory waste problem if we define field on struct page_ext by
hard-coding. Entry size of struct page_ext includes the size of those
fields even if it is disabled at runtime. Now, extra memory request at
runtime is possible so page_owner don't need to define it's own fields
by hard-coding.

This patch removes hard-coded define and uses extra memory for storing
page_owner information in page_owner. Most of code are just mechanical
changes.

Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Joonsoo Kim <[e-mail]>
Acked-by: Vlastimil Babka <[e-mail]>
Cc: Minchan Kim <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: Sergey Senozhatsky <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/page_ext.h

···
  */
 struct page_ext {
 	unsigned long flags;
-#ifdef CONFIG_PAGE_OWNER
-	unsigned int order;
-	gfp_t gfp_mask;
-	int last_migrate_reason;
-	depot_stack_handle_t handle;
-#endif
 };
 
 extern void pgdat_page_ext_init(struct pglist_data *pgdat);

mm/page_owner.c

···
  */
 #define PAGE_OWNER_STACK_DEPTH (16)
 
+struct page_owner {
+	unsigned int order;
+	gfp_t gfp_mask;
+	int last_migrate_reason;
+	depot_stack_handle_t handle;
+};
+
 static bool page_owner_disabled = true;
 DEFINE_STATIC_KEY_FALSE(page_owner_inited);
 
···
 }
 
 struct page_ext_operations page_owner_ops = {
+	.size = sizeof(struct page_owner),
 	.need = need_page_owner,
 	.init = init_page_owner,
 };
+
+static inline struct page_owner *get_page_owner(struct page_ext *page_ext)
+{
+	return (void *)page_ext + page_owner_ops.offset;
+}
 
 void __reset_page_owner(struct page *page, unsigned int order)
 {
···
 					gfp_t gfp_mask)
 {
 	struct page_ext *page_ext = lookup_page_ext(page);
+	struct page_owner *page_owner;
 
 	if (unlikely(!page_ext))
 		return;
 
-	page_ext->handle = save_stack(gfp_mask);
-	page_ext->order = order;
-	page_ext->gfp_mask = gfp_mask;
-	page_ext->last_migrate_reason = -1;
+	page_owner = get_page_owner(page_ext);
+	page_owner->handle = save_stack(gfp_mask);
+	page_owner->order = order;
+	page_owner->gfp_mask = gfp_mask;
+	page_owner->last_migrate_reason = -1;
 
 	__set_bit(PAGE_EXT_OWNER, &page_ext->flags);
 }
···
 void __set_page_owner_migrate_reason(struct page *page, int reason)
 {
 	struct page_ext *page_ext = lookup_page_ext(page);
+	struct page_owner *page_owner;
+
 	if (unlikely(!page_ext))
 		return;
 
-	page_ext->last_migrate_reason = reason;
+	page_owner = get_page_owner(page_ext);
+	page_owner->last_migrate_reason = reason;
 }
 
 void __split_page_owner(struct page *page, unsigned int order)
 {
 	int i;
 	struct page_ext *page_ext = lookup_page_ext(page);
+	struct page_owner *page_owner;
 
 	if (unlikely(!page_ext))
 		return;
 
-	page_ext->order = 0;
+	page_owner = get_page_owner(page_ext);
+	page_owner->order = 0;
 	for (i = 1; i < (1 << order); i++)
 		__copy_page_owner(page, page + i);
 }
···
 {
 	struct page_ext *old_ext = lookup_page_ext(oldpage);
 	struct page_ext *new_ext = lookup_page_ext(newpage);
+	struct page_owner *old_page_owner, *new_page_owner;
 
 	if (unlikely(!old_ext || !new_ext))
 		return;
 
-	new_ext->order = old_ext->order;
-	new_ext->gfp_mask = old_ext->gfp_mask;
-	new_ext->last_migrate_reason = old_ext->last_migrate_reason;
-	new_ext->handle = old_ext->handle;
+	old_page_owner = get_page_owner(old_ext);
+	new_page_owner = get_page_owner(new_ext);
+	new_page_owner->order = old_page_owner->order;
+	new_page_owner->gfp_mask = old_page_owner->gfp_mask;
+	new_page_owner->last_migrate_reason =
+		old_page_owner->last_migrate_reason;
+	new_page_owner->handle = old_page_owner->handle;
 
 	/*
 	 * We don't clear the bit on the oldpage as it's going to be freed
···
 {
 	struct page *page;
 	struct page_ext *page_ext;
+	struct page_owner *page_owner;
 	unsigned long pfn = zone->zone_start_pfn, block_end_pfn;
 	unsigned long end_pfn = pfn + zone->spanned_pages;
 	unsigned long count[MIGRATE_TYPES] = { 0, };
···
 			if (!test_bit(PAGE_EXT_OWNER, &page_ext->flags))
 				continue;
 
-			page_mt = gfpflags_to_migratetype(page_ext->gfp_mask);
+			page_owner = get_page_owner(page_ext);
+			page_mt = gfpflags_to_migratetype(
+					page_owner->gfp_mask);
 			if (pageblock_mt != page_mt) {
 				if (is_migrate_cma(pageblock_mt))
 					count[MIGRATE_MOVABLE]++;
···
 				pfn = block_end_pfn;
 				break;
 			}
-			pfn += (1UL << page_ext->order) - 1;
+			pfn += (1UL << page_owner->order) - 1;
 		}
 	}
 
···
 
 static ssize_t
 print_page_owner(char __user *buf, size_t count, unsigned long pfn,
-		struct page *page, struct page_ext *page_ext,
+		struct page *page, struct page_owner *page_owner,
 		depot_stack_handle_t handle)
 {
 	int ret;
···
 
 	ret = snprintf(kbuf, count,
 			"Page allocated via order %u, mask %#x(%pGg)\n",
-			page_ext->order, page_ext->gfp_mask,
-			&page_ext->gfp_mask);
+			page_owner->order, page_owner->gfp_mask,
+			&page_owner->gfp_mask);
 
 	if (ret >= count)
 		goto err;
 
 	/* Print information relevant to grouping pages by mobility */
 	pageblock_mt = get_pageblock_migratetype(page);
-	page_mt  = gfpflags_to_migratetype(page_ext->gfp_mask);
+	page_mt  = gfpflags_to_migratetype(page_owner->gfp_mask);
 	ret += snprintf(kbuf + ret, count - ret,
 			"PFN %lu type %s Block %lu type %s Flags %#lx(%pGp)\n",
 			pfn,
···
 	if (ret >= count)
 		goto err;
 
-	if (page_ext->last_migrate_reason != -1) {
+	if (page_owner->last_migrate_reason != -1) {
 		ret += snprintf(kbuf + ret, count - ret,
 			"Page has been migrated, last migrate reason: %s\n",
-			migrate_reason_names[page_ext->last_migrate_reason]);
+			migrate_reason_names[page_owner->last_migrate_reason]);
 		if (ret >= count)
 			goto err;
 	}
···
 void __dump_page_owner(struct page *page)
 {
 	struct page_ext *page_ext = lookup_page_ext(page);
+	struct page_owner *page_owner;
 	unsigned long entries[PAGE_OWNER_STACK_DEPTH];
 	struct stack_trace trace = {
 		.nr_entries = 0,
···
 		pr_alert("There is not page extension available.\n");
 		return;
 	}
-	gfp_mask = page_ext->gfp_mask;
+
+	page_owner = get_page_owner(page_ext);
+	gfp_mask = page_owner->gfp_mask;
 	mt = gfpflags_to_migratetype(gfp_mask);
 
 	if (!test_bit(PAGE_EXT_OWNER, &page_ext->flags)) {
···
 		return;
 	}
 
-	handle = READ_ONCE(page_ext->handle);
+	handle = READ_ONCE(page_owner->handle);
 	if (!handle) {
 		pr_alert("page_owner info is not active (free page?)\n");
 		return;
···
 
 	depot_fetch_stack(handle, &trace);
 	pr_alert("page allocated via order %u, migratetype %s, gfp_mask %#x(%pGg)\n",
-		 page_ext->order, migratetype_names[mt], gfp_mask, &gfp_mask);
+		 page_owner->order, migratetype_names[mt], gfp_mask, &gfp_mask);
 	print_stack_trace(&trace, 0);
 
-	if (page_ext->last_migrate_reason != -1)
+	if (page_owner->last_migrate_reason != -1)
 		pr_alert("page has been migrated, last migrate reason: %s\n",
-			migrate_reason_names[page_ext->last_migrate_reason]);
+			migrate_reason_names[page_owner->last_migrate_reason]);
 }
 
 static ssize_t
···
 	unsigned long pfn;
 	struct page *page;
 	struct page_ext *page_ext;
+	struct page_owner *page_owner;
 	depot_stack_handle_t handle;
 
 	if (!static_branch_unlikely(&page_owner_inited))
···
 		if (!test_bit(PAGE_EXT_OWNER, &page_ext->flags))
 			continue;
 
+		page_owner = get_page_owner(page_ext);
+
 		/*
 		 * Access to page_ext->handle isn't synchronous so we should
 		 * be careful to access it.
 		 */
-		handle = READ_ONCE(page_ext->handle);
+		handle = READ_ONCE(page_owner->handle);
 		if (!handle)
 			continue;
 
···
 		*ppos = (pfn - min_low_pfn) + 1;
 
 		return print_page_owner(buf, count, pfn, page,
-				page_ext, handle);
+				page_owner, handle);
 	}
 
 	return 0;