Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
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, aaron.lwe@gmail.com
Cc:     =?UTF-8?q?Mika=20Penttil=C3=A4?= <mika.penttila@nextfour.com>
Subject: [PATCH v19 05/20] mm/thp: Simplify lru_add_page_tail()
Date:   Thu, 24 Sep 2020 11:28:20 +0800
Message-Id: <1600918115-22007-6-git-send-email-alex.shi@linux.alibaba.com>
In-Reply-To: <1600918115-22007-1-git-send-email-alex.shi@linux.alibaba.com>
References: <1600918115-22007-1-git-send-email-alex.shi@linux.alibaba.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Precedence: bulk

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 | 21 ++++++---------------
 1 file changed, 6 insertions(+), 15 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index fa0753229b52..8b92cd197218 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2326,25 +2326,16 @@ static void lru_add_page_tail(struct page *head, struct page *page_tail,
 	VM_BUG_ON_PAGE(PageLRU(page_tail), head);
 	lockdep_assert_held(&lruvec_pgdat(lruvec)->lru_lock);
 
-	if (!list)
-		SetPageLRU(page_tail);
-
-	if (likely(PageLRU(head)))
-		list_add_tail(&page_tail->lru, &head->lru);
-	else if (list) {
+	if (list) {
 		/* page reclaim is reclaiming a huge page */
+		VM_WARN_ON(PageLRU(head));
 		get_page(page_tail);
 		list_add_tail(&page_tail->lru, list);
 	} else {
-		/*
-		 * Head page has not yet been counted, as an hpage,
-		 * so we must account for each subpage individually.
-		 *
-		 * Put page_tail on the list at the correct position
-		 * so they all end up in order.
-		 */
-		add_page_to_lru_list_tail(page_tail, lruvec,
-					  page_lru(page_tail));
+		/* head is still on lru (and we have it frozen) */
+		VM_WARN_ON(!PageLRU(head));
+		SetPageLRU(page_tail);
+		list_add_tail(&page_tail->lru, &head->lru);
 	}
 }
 
-- 
1.8.3.1