[PATCH v21 03/19] mm/thp: Simplify lru_add_page_tail()

From: Alex Shi <alex.shi@linux.alibaba.com>
To: akpm@linux-foundation.org, mgorman@techsingularity.net,
	tj@kernel.org, hughd@google.com, khlebnikov@yandex-team.ru,
	daniel.m.jordan@oracle.com, willy@infradead.org,
	hannes@cmpxchg.org, lkp@intel.com, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
	shakeelb@google.com, iamjoonsoo.kim@lge.com,
	richard.weiyang@gmail.com, kirill@shutemov.name,
	alexander.duyck@gmail.com, rong.a.chen@intel.com,
	mhocko@suse.com, vdavydov.dev@gmail.com, shy828301@gmail.com
Cc: "Mika Penttilä" <mika.penttila@nextfour.com>
Subject: [PATCH v21 03/19] mm/thp: Simplify lru_add_page_tail()
Date: Thu,  5 Nov 2020 16:55:33 +0800	[thread overview]
Message-ID: <1604566549-62481-4-git-send-email-alex.shi@linux.alibaba.com> (raw)
In-Reply-To: <1604566549-62481-1-git-send-email-alex.shi@linux.alibaba.com>

Simplify lru_add_page_tail(), there are actually only two cases possible:
split_huge_page_to_list(), with list supplied and head isolated from lru
by its caller; or split_huge_page(), with NULL list and head on lru -
because when head is racily isolated from lru, the isolator's reference
will stop the split from getting any further than its page_ref_freeze().

So decide between the two cases by "list", but add VM_WARN_ON()s to
verify that they match our lru expectations.

[Hugh Dickins: rewrite commit log]
Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Mika Penttilä <mika.penttila@nextfour.com>
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
---
 mm/huge_memory.c | 20 ++++++--------------
 1 file changed, 6 insertions(+), 14 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 60726eb26840..79318d7f7d5d 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2356,24 +2356,16 @@ static void lru_add_page_tail(struct page *head, struct page *tail,
 	VM_BUG_ON_PAGE(PageLRU(tail), head);
 	lockdep_assert_held(&lruvec_pgdat(lruvec)->lru_lock);
 
-	if (!list)
-		SetPageLRU(tail);
-
-	if (likely(PageLRU(head)))
-		list_add_tail(&tail->lru, &head->lru);
-	else if (list) {
+	if (list) {
 		/* page reclaim is reclaiming a huge page */
+		VM_WARN_ON(PageLRU(head));
 		get_page(tail);
 		list_add_tail(&tail->lru, list);
 	} else {
-		/*
-		 * Head page has not yet been counted, as an hpage,
-		 * so we must account for each subpage individually.
-		 *
-		 * Put tail on the list at the correct position
-		 * so they all end up in order.
-		 */
-		add_page_to_lru_list_tail(tail, lruvec, page_lru(tail));
+		/* head is still on lru (and we have it frozen) */
+		VM_WARN_ON(!PageLRU(head));
+		SetPageLRU(tail);
+		list_add_tail(&tail->lru, &head->lru);
 	}
 }
 
-- 
1.8.3.1

