mm: thp: extract split_queue_* into a struct

Patch series "Make deferred split shrinker memcg aware", v6.

Currently THP deferred split shrinker is not memcg aware, this may cause
premature OOM with some configuration.  For example the below test would
run into premature OOM easily:

$ cgcreate -g memory:thp
$ echo 4G > /sys/fs/cgroup/memory/thp/memory/limit_in_bytes
$ cgexec -g memory:thp transhuge-stress 4000

transhuge-stress comes from kernel selftest.

It is easy to hit OOM, but there are still a lot THP on the deferred split
queue, memcg direct reclaim can't touch them since the deferred split
shrinker is not memcg aware.

Convert deferred split shrinker memcg aware by introducing per memcg
deferred split queue.  The THP should be on either per node or per memcg
deferred split queue if it belongs to a memcg.  When the page is
immigrated to the other memcg, it will be immigrated to the target memcg's
deferred split queue too.

Reuse the second tail page's deferred_list for per memcg list since the
same THP can't be on multiple deferred split queues.

Make deferred split shrinker not depend on memcg kmem since it is not
slab.  It doesn't make sense to not shrink THP even though memcg kmem is
disabled.

With the above change the test demonstrated above doesn't trigger OOM even
though with cgroup.memory=nokmem.

This patch (of 4):

Put split_queue, split_queue_lock and split_queue_len into a struct in
order to reduce code duplication when we convert deferred_split to memcg
aware in the later patches.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Yang Shi <[email protected]>
Suggested-by: "Kirill A . Shutemov" <[email protected]>
Acked-by: Kirill A. Shutemov <[email protected]>
Reviewed-by: Kirill Tkhai <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Shakeel Butt <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Qian Cai <[email protected]>
Cc: Vladimir Davydov <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: Yang Shi

include/linux/mmzone.h

@@ -679,6 +679,14 @@ struct zonelist {
 extern struct page *mem_map;
 #endif
 
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+struct deferred_split {
+	spinlock_t split_queue_lock;
+	struct list_head split_queue;
+	unsigned long split_queue_len;
+};
+#endif
+
 /*
  * On NUMA machines, each NUMA node would have a pg_data_t to describe
  * it's memory layout. On UMA machines there is a single pglist_data which
@@ -758,9 +766,7 @@ typedef struct pglist_data {
 #endif /* CONFIG_DEFERRED_STRUCT_PAGE_INIT */
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	spinlock_t split_queue_lock;
-	struct list_head split_queue;
-	unsigned long split_queue_len;
+	struct deferred_split deferred_split_queue;
 #endif
 
 	/* Fields commonly accessed by the page reclaim scanner */

mm/huge_memory.c

@@ -2691,6 +2691,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
 {
 	struct page *head = compound_head(page);
 	struct pglist_data *pgdata = NODE_DATA(page_to_nid(head));
+	struct deferred_split *ds_queue = &pgdata->deferred_split_queue;
 	struct anon_vma *anon_vma = NULL;
 	struct address_space *mapping = NULL;
 	int count, mapcount, extra_pins, ret;
@@ -2777,17 +2778,17 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
 	}
 
 	/* Prevent deferred_split_scan() touching ->_refcount */
-	spin_lock(&pgdata->split_queue_lock);
+	spin_lock(&ds_queue->split_queue_lock);
 	count = page_count(head);
 	mapcount = total_mapcount(head);
 	if (!mapcount && page_ref_freeze(head, 1 + extra_pins)) {
 		if (!list_empty(page_deferred_list(head))) {
-			pgdata->split_queue_len--;
+			ds_queue->split_queue_len--;
 			list_del(page_deferred_list(head));
 		}
 		if (mapping)
 			__dec_node_page_state(page, NR_SHMEM_THPS);
-		spin_unlock(&pgdata->split_queue_lock);
+		spin_unlock(&ds_queue->split_queue_lock);
 		__split_huge_page(page, list, end, flags);
 		if (PageSwapCache(head)) {
 			swp_entry_t entry = { .val = page_private(head) };
@@ -2804,7 +2805,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
 			dump_page(page, "total_mapcount(head) > 0");
 			BUG();
 		}
-		spin_unlock(&pgdata->split_queue_lock);
+		spin_unlock(&ds_queue->split_queue_lock);
 fail:		if (mapping)
 			xa_unlock(&mapping->i_pages);
 		spin_unlock_irqrestore(&pgdata->lru_lock, flags);
@@ -2827,65 +2828,69 @@ fail:		if (mapping)
 void free_transhuge_page(struct page *page)
 {
 	struct pglist_data *pgdata = NODE_DATA(page_to_nid(page));
+	struct deferred_split *ds_queue = &pgdata->deferred_split_queue;
 	unsigned long flags;
 
-	spin_lock_irqsave(&pgdata->split_queue_lock, flags);
+	spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
 	if (!list_empty(page_deferred_list(page))) {
-		pgdata->split_queue_len--;
+		ds_queue->split_queue_len--;
 		list_del(page_deferred_list(page));
 	}
-	spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
+	spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
 	free_compound_page(page);
 }
 
 void deferred_split_huge_page(struct page *page)
 {
 	struct pglist_data *pgdata = NODE_DATA(page_to_nid(page));
+	struct deferred_split *ds_queue = &pgdata->deferred_split_queue;
 	unsigned long flags;
 
 	VM_BUG_ON_PAGE(!PageTransHuge(page), page);
 
-	spin_lock_irqsave(&pgdata->split_queue_lock, flags);
+	spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
 	if (list_empty(page_deferred_list(page))) {
 		count_vm_event(THP_DEFERRED_SPLIT_PAGE);
-		list_add_tail(page_deferred_list(page), &pgdata->split_queue);
-		pgdata->split_queue_len++;
+		list_add_tail(page_deferred_list(page), &ds_queue->split_queue);
+		ds_queue->split_queue_len++;
 	}
-	spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
+	spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
 }
 
 static unsigned long deferred_split_count(struct shrinker *shrink,
 		struct shrink_control *sc)
 {
 	struct pglist_data *pgdata = NODE_DATA(sc->nid);
-	return READ_ONCE(pgdata->split_queue_len);
+	struct deferred_split *ds_queue = &pgdata->deferred_split_queue;
+	return READ_ONCE(ds_queue->split_queue_len);
 }
 
 static unsigned long deferred_split_scan(struct shrinker *shrink,
 		struct shrink_control *sc)
 {
 	struct pglist_data *pgdata = NODE_DATA(sc->nid);
+	struct deferred_split *ds_queue = &pgdata->deferred_split_queue;
 	unsigned long flags;
 	LIST_HEAD(list), *pos, *next;
 	struct page *page;
 	int split = 0;
 
-	spin_lock_irqsave(&pgdata->split_queue_lock, flags);
+	spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
 	/* Take pin on all head pages to avoid freeing them under us */
-	list_for_each_safe(pos, next, &pgdata->split_queue) {
+	list_for_each_safe(pos, next, &ds_queue->split_queue) {
 		page = list_entry((void *)pos, struct page, mapping);
 		page = compound_head(page);
 		if (get_page_unless_zero(page)) {
 			list_move(page_deferred_list(page), &list);
 		} else {
 			/* We lost race with put_compound_page() */
 			list_del_init(page_deferred_list(page));
-			pgdata->split_queue_len--;
+			ds_queue->split_queue_len--;
 		}
 		if (!--sc->nr_to_scan)
 			break;
 	}
-	spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
+	spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
 
 	list_for_each_safe(pos, next, &list) {
 		page = list_entry((void *)pos, struct page, mapping);
@@ -2899,15 +2904,15 @@ static unsigned long deferred_split_scan(struct shrinker *shrink,
 		put_page(page);
 	}
 
-	spin_lock_irqsave(&pgdata->split_queue_lock, flags);
-	list_splice_tail(&list, &pgdata->split_queue);
-	spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
+	spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
+	list_splice_tail(&list, &ds_queue->split_queue);
+	spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
 
 	/*
 	 * Stop shrinker if we didn't split any page, but the queue is empty.
 	 * This can happen if pages were freed under us.
 	 */
-	if (!split && list_empty(&pgdata->split_queue))
+	if (!split && list_empty(&ds_queue->split_queue))
 		return SHRINK_STOP;
 	return split;
 }

mm/page_alloc.c

@@ -6646,9 +6646,11 @@ static unsigned long __init calc_memmap_size(unsigned long spanned_pages,
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 static void pgdat_init_split_queue(struct pglist_data *pgdat)
 {
-	spin_lock_init(&pgdat->split_queue_lock);
-	INIT_LIST_HEAD(&pgdat->split_queue);
-	pgdat->split_queue_len = 0;
+	struct deferred_split *ds_queue = &pgdat->deferred_split_queue;
+
+	spin_lock_init(&ds_queue->split_queue_lock);
+	INIT_LIST_HEAD(&ds_queue->split_queue);
+	ds_queue->split_queue_len = 0;
 }
 #else
 static void pgdat_init_split_queue(struct pglist_data *pgdat) {}