[patch 03/19] mm/thp: simplify lru_add_page_tail()

From: Andrew Morton <akpm@linux-foundation.org>
To: aarcange@redhat.com, akpm@linux-foundation.org,
	alex.shi@linux.alibaba.com, alexander.duyck@gmail.com,
	aryabinin@virtuozzo.com, daniel.m.jordan@oracle.com,
	hannes@cmpxchg.org, hughd@google.com, iamjoonsoo.kim@lge.com,
	jannh@google.com, khlebnikov@yandex-team.ru,
	kirill.shutemov@linux.intel.com, kirill@shutemov.name,
	linux-mm@kvack.org, mgorman@techsingularity.net,
	mhocko@kernel.org, mhocko@suse.com, mika.penttila@nextfour.com,
	minchan@kernel.org, mm-commits@vger.kernel.org,
	richard.weiyang@gmail.com, rong.a.chen@intel.com,
	shakeelb@google.com, tglx@linutronix.de, tj@kernel.org,
	torvalds@linux-foundation.org, vbabka@suse.cz,
	vdavydov.dev@gmail.com, willy@infradead.org,
	yang.shi@linux.alibaba.com, ying.huang@intel.com
Subject: [patch 03/19] mm/thp: simplify lru_add_page_tail()
Date: Tue, 15 Dec 2020 12:33:29 -0800	[thread overview]
Message-ID: <20201215203329.o2h4X80q8%akpm@linux-foundation.org> (raw)
In-Reply-To: <20201215123253.954eca9a5ef4c0d52fd381fa@linux-foundation.org>

From: Alex Shi <alex.shi@linux.alibaba.com>
Subject: mm/thp: simplify lru_add_page_tail()

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]
Link: https://lkml.kernel.org/r/1604566549-62481-4-git-send-email-alex.shi@linux.alibaba.com
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: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mika Penttilä <mika.penttila@nextfour.com>
Cc: Alexander Duyck <alexander.duyck@gmail.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: "Chen, Rong A" <rong.a.chen@intel.com>
Cc: Daniel Jordan <daniel.m.jordan@oracle.com>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Jann Horn <jannh@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Wei Yang <richard.weiyang@gmail.com>
Cc: Yang Shi <yang.shi@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/huge_memory.c |   20 ++++++--------------
 1 file changed, 6 insertions(+), 14 deletions(-)

--- a/mm/huge_memory.c~mm-thp-simplify-lru_add_page_tail
+++ a/mm/huge_memory.c
@@ -2367,24 +2367,16 @@ static void lru_add_page_tail(struct pag
 	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);
 	}
 }
 
_
