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Subject[PATCH v19 08/20] mm: page_idle_get_page() does not need lru_lock
From: Hugh Dickins <>

It is necessary for page_idle_get_page() to recheck PageLRU() after
get_page_unless_zero(), but holding lru_lock around that serves no
useful purpose, and adds to lru_lock contention: delete it.

See for the
discussion that led to lru_lock there; but __page_set_anon_rmap() now
uses WRITE_ONCE(), and I see no other risk in page_idle_clear_pte_refs()
using rmap_walk() (beyond the risk of racing PageAnon->PageKsm, mostly
but not entirely prevented by page_count() check in ksm.c's
write_protect_page(): that risk being shared with page_referenced() and
not helped by lru_lock).

Signed-off-by: Hugh Dickins <>
Signed-off-by: Alex Shi <>
Cc: Andrew Morton <>
Cc: Vladimir Davydov <>
Cc: Vlastimil Babka <>
Cc: Minchan Kim <>
Cc: Alex Shi <>
mm/page_idle.c | 4 ----
1 file changed, 4 deletions(-)

diff --git a/mm/page_idle.c b/mm/page_idle.c
index 057c61df12db..64e5344a992c 100644
--- a/mm/page_idle.c
+++ b/mm/page_idle.c
@@ -32,19 +32,15 @@
static struct page *page_idle_get_page(unsigned long pfn)
struct page *page = pfn_to_online_page(pfn);
- pg_data_t *pgdat;

if (!page || !PageLRU(page) ||
return NULL;

- pgdat = page_pgdat(page);
- spin_lock_irq(&pgdat->lru_lock);
if (unlikely(!PageLRU(page))) {
page = NULL;
- spin_unlock_irq(&pgdat->lru_lock);
return page;

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