linux-kernel - Re: [PATCH v20 05/20] mm/thp: Simplify lru_add_page

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Date:   Fri, 30 Oct 2020 10:48:25 +0800
From:   Alex Shi <alex.shi@...ux.alibaba.com>
To:     akpm@...ux-foundation.org, mgorman@...hsingularity.net,
        tj@...nel.org, hughd@...gle.com, khlebnikov@...dex-team.ru,
        daniel.m.jordan@...cle.com, willy@...radead.org,
        hannes@...xchg.org, lkp@...el.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        shakeelb@...gle.com, iamjoonsoo.kim@....com,
        richard.weiyang@...il.com, kirill@...temov.name,
        alexander.duyck@...il.com, rong.a.chen@...el.com, mhocko@...e.com,
        vdavydov.dev@...il.com, shy828301@...il.com
Cc:     Mika Penttilä <mika.penttila@...tfour.com>
Subject: Re: [PATCH v20 05/20] mm/thp: Simplify lru_add_page_tail()

patch changed since varible rename in 4th patch:

>From 5014c78418284f70be232a37fa3a4660a54e83c0 Mon Sep 17 00:00:00 2001
From: Alex Shi <alex.shi@...ux.alibaba.com>
Date: Fri, 10 Jul 2020 12:53:22 +0800
Subject: [PATCH v21 05/20] mm/thp: Simplify lru_add_page_tail()
MIME-Version: 1.0
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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@...ux.alibaba.com>
Reviewed-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Acked-by: Hugh Dickins <hughd@...gle.com>
Cc: Kirill A. Shutemov <kirill@...temov.name>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Johannes Weiner <hannes@...xchg.org>
Cc: Matthew Wilcox <willy@...radead.org>
Cc: Hugh Dickins <hughd@...gle.com>
Cc: Mika Penttilä <mika.penttila@...tfour.com>
Cc: linux-mm@...ck.org
Cc: linux-kernel@...r.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 32a4bf5b80c8..cedcdbeb98b4 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2354,24 +2354,16 @@ 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