Re: [PATCH v20 05/20] mm/thp: Simplify lru_add_page_tail()

Alex Shi
2020-10-30T02:50:41Z

patch changed since varible rename in 4th patch:

From 5014c78418284f70be232a37fa3a4660a54e83c0 Mon Sep 17 00:00:00 2001
From: Alex Shi <alex.shi@linux.alibaba.com>
Date: Fri, 10 Jul 2020 12:53:22 +0800
Subject: [PATCH v21 05/20] mm/thp: Simplify lru_add_page_tail()
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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@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 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