mm: thp: add split tail pages to shrink page list in page reclaim

In page reclaim, huge page is split.  split_huge_page() adds tail pages
to LRU list.  Since we are reclaiming a huge page, it's better we
reclaim all subpages of the huge page instead of just the head page.
This patch adds split tail pages to shrink page list so the tail pages
can be reclaimed soon.

Before this patch, run a swap workload:
  thp_fault_alloc 3492
  thp_fault_fallback 608
  thp_collapse_alloc 6
  thp_collapse_alloc_failed 0
  thp_split 916

With this patch:
  thp_fault_alloc 4085
  thp_fault_fallback 16
  thp_collapse_alloc 90
  thp_collapse_alloc_failed 0
  thp_split 1272

fallback allocation is reduced a lot.

[akpm@linux-foundation.org: fix CONFIG_SWAP=n build]
Signed-off-by: Shaohua Li <shli@fusionio.com>
Acked-by: Rik van Riel <riel@redhat.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 8 insertions, 3 deletions

diff --git a/mm/swap.c b/mm/swap.c
index 8a529a0..acd40bf 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -737,7 +737,7 @@ EXPORT_SYMBOL(__pagevec_release);
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 /* used by __split_huge_page_refcount() */
 void lru_add_page_tail(struct page *page, struct page *page_tail,
-		       struct lruvec *lruvec)
+		       struct lruvec *lruvec, struct list_head *list)
 {
 	int uninitialized_var(active);
 	enum lru_list lru;
@@ -749,7 +749,8 @@ void lru_add_page_tail(struct page *page, struct page *page_tail,
 	VM_BUG_ON(NR_CPUS != 1 &&
 		  !spin_is_locked(&lruvec_zone(lruvec)->lru_lock));
 
-	SetPageLRU(page_tail);
+	if (!list)
+		SetPageLRU(page_tail);
 
 	if (page_evictable(page_tail)) {
 		if (PageActive(page)) {
@@ -767,7 +768,11 @@ void lru_add_page_tail(struct page *page, struct page *page_tail,
 
 	if (likely(PageLRU(page)))
 		list_add_tail(&page_tail->lru, &page->lru);
-	else {
+	else if (list) {
+		/* page reclaim is reclaiming a huge page */
+		get_page(page_tail);
+		list_add_tail(&page_tail->lru, list);
+	} else {
 		struct list_head *list_head;
 		/*
 		 * Head page has not yet been counted, as an hpage,