[PATCH 06/10] mm: remove unnecessary use-once cache bias from LRU balancing

[Johannes Weiner <hannes@xxxxxxxxxxx>]

When the splitlru patches divided page cache and swap-backed pages
into separate LRU lists, the pressure balance between the lists was
biased to account for the fact that streaming IO can cause memory
pressure with a flood of pages that are used only once. New page cache
additions would tip the balance toward the file LRU, and repeat access
would neutralize that bias again. This ensured that page reclaim would
always go for used-once cache first.

Since e9868505987a ("mm,vmscan: only evict file pages when we have
plenty"), page reclaim generally skips over swap-backed memory
entirely as long as there is used-once cache present, and will apply
the LRU balancing when only repeatedly accessed cache pages are left -
at which point the previous use-once bias will have been neutralized.

This makes the use-once cache balancing bias unnecessary. Remove it.

Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
---
 mm/swap.c | 11 -----------
 1 file changed, 11 deletions(-)

diff --git a/mm/swap.c b/mm/swap.c
index 576c721f210b..814e3a2e54b4 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -264,7 +264,6 @@ static void __activate_page(struct page *page, struct lruvec *lruvec,
 			    void *arg)
 {
 	if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
-		int file = page_is_file_cache(page);
 		int lru = page_lru_base_type(page);
 
 		del_page_from_lru_list(page, lruvec, lru);
@@ -274,7 +273,6 @@ static void __activate_page(struct page *page, struct lruvec *lruvec,
 		trace_mm_lru_activate(page);
 
 		__count_vm_event(PGACTIVATE);
-		update_page_reclaim_stat(lruvec, file, 1, hpage_nr_pages(page));
 	}
 }
 
@@ -797,8 +795,6 @@ EXPORT_SYMBOL(__pagevec_release);
 void lru_add_page_tail(struct page *page, struct page *page_tail,
 		       struct lruvec *lruvec, struct list_head *list)
 {
-	const int file = 0;
-
 	VM_BUG_ON_PAGE(!PageHead(page), page);
 	VM_BUG_ON_PAGE(PageCompound(page_tail), page);
 	VM_BUG_ON_PAGE(PageLRU(page_tail), page);
@@ -833,20 +829,13 @@ void lru_add_page_tail(struct page *page, struct page *page_tail,
 static void __pagevec_lru_add_fn(struct page *page, struct lruvec *lruvec,
 				 void *arg)
 {
-	int file = page_is_file_cache(page);
-	int active = PageActive(page);
 	enum lru_list lru = page_lru(page);
-	bool new = (bool)arg;
 
 	VM_BUG_ON_PAGE(PageLRU(page), page);
 
 	SetPageLRU(page);
 	add_page_to_lru_list(page, lruvec, lru);
 
-	if (new)
-		update_page_reclaim_stat(lruvec, file, active,
-					 hpage_nr_pages(page));
-
 	trace_mm_lru_insertion(page, lru);
 }
 
-- 
2.8.3

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