[v13,07/18] mm/thp: narrow lru locking

Commit Message

Alex Shi June 19, 2020, 8:33 a.m. UTC

lru_lock and page cache xa_lock have no reason with current sequence,
put them together isn't necessary. let's narrow the lru locking, but
left the local_irq_disable to block interrupt re-entry and statistic update.

Hugh Dickins point: split_huge_page_to_list() was already silly,to be
using the _irqsave variant: it's just been taking sleeping locks, so
would already be broken if entered with interrupts enabled.
so we can save passing flags argument down to __split_huge_page().

Signed-off-by: Alex Shi <[e-mail]>
Signed-off-by: Wei Yang <[e-mail]>
Cc: Hugh Dickins <[e-mail]>
Cc: Kirill A. Shutemov <[e-mail]>
Cc: Andrea Arcangeli <[e-mail]>
Cc: Johannes Weiner <[e-mail]>
Cc: Matthew Wilcox <[e-mail]>
Cc: Andrew Morton <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
---
 mm/huge_memory.c | 25 +++++++++++++------------
 1 file changed, 13 insertions(+), 12 deletions(-)

Patch

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index b18f21da4dac..b660550f0e9a 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2433,17 +2433,16 @@  static void __split_huge_page_tail(struct page *head, int tail,
 }
 
 static void __split_huge_page(struct page *page, struct list_head *list,
-		pgoff_t end, unsigned long flags)
+			      pgoff_t end)
 {
 	struct page *head = compound_head(page);
 	pg_data_t *pgdat = page_pgdat(head);
 	struct lruvec *lruvec;
 	struct address_space *swap_cache = NULL;
 	unsigned long offset = 0;
+	unsigned long flags;
 	int i;
 
-	lruvec = mem_cgroup_page_lruvec(head, pgdat);
-
 	/* complete memcg works before add pages to LRU */
 	mem_cgroup_split_huge_fixup(head);
 
@@ -2455,6 +2454,11 @@  static void __split_huge_page(struct page *page, struct list_head *list,
 		xa_lock(&swap_cache->i_pages);
 	}
 
+	/* lock lru list/PageCompound, ref freezed by page_ref_freeze */
+	spin_lock_irqsave(&pgdat->lru_lock, &flags);
+
+	lruvec = mem_cgroup_page_lruvec(head, pgdat);
+
 	for (i = HPAGE_PMD_NR - 1; i >= 1; i--) {
 		__split_huge_page_tail(head, i, lruvec, list);
 		/* Some pages can be beyond i_size: drop them from page cache */
@@ -2474,6 +2478,8 @@  static void __split_huge_page(struct page *page, struct list_head *list,
 	}
 
 	ClearPageCompound(head);
+	spin_unlock_irqrestore(&pgdat->lru_lock, flags);
+	/* Caller disabled irqs, so they are still disabled here */
 
 	split_page_owner(head, HPAGE_PMD_ORDER);
 
@@ -2491,8 +2497,7 @@  static void __split_huge_page(struct page *page, struct list_head *list,
 		page_ref_add(head, 2);
 		xa_unlock(&head->mapping->i_pages);
 	}
-
-	spin_unlock_irqrestore(&pgdat->lru_lock, flags);
+	local_irq_enable();
 
 	remap_page(head);
 
@@ -2631,12 +2636,10 @@  bool can_split_huge_page(struct page *page, int *pextra_pins)
 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 = get_deferred_split_queue(head);
 	struct anon_vma *anon_vma = NULL;
 	struct address_space *mapping = NULL;
 	int count, mapcount, extra_pins, ret;
-	unsigned long flags;
 	pgoff_t end;
 
 	VM_BUG_ON_PAGE(is_huge_zero_page(head), head);
@@ -2697,9 +2700,7 @@  int split_huge_page_to_list(struct page *page, struct list_head *list)
 	unmap_page(head);
 	VM_BUG_ON_PAGE(compound_mapcount(head), head);
 
-	/* prevent PageLRU to go away from under us, and freeze lru stats */
-	spin_lock_irqsave(&pgdata->lru_lock, flags);
-
+	local_irq_disable();
 	if (mapping) {
 		XA_STATE(xas, &mapping->i_pages, page_index(head));
 
@@ -2729,7 +2730,7 @@  int split_huge_page_to_list(struct page *page, struct list_head *list)
 				__dec_node_page_state(head, NR_FILE_THPS);
 		}
 
-		__split_huge_page(page, list, end, flags);
+		__split_huge_page(page, list, end);
 		if (PageSwapCache(head)) {
 			swp_entry_t entry = { .val = page_private(head) };
 
@@ -2748,7 +2749,7 @@  int split_huge_page_to_list(struct page *page, struct list_head *list)
 		spin_unlock(&ds_queue->split_queue_lock);
 fail:		if (mapping)
 			xa_unlock(&mapping->i_pages);
-		spin_unlock_irqrestore(&pgdata->lru_lock, flags);
+		local_irq_enable();
 		remap_page(head);
 		ret = -EBUSY;
 	}