From: Hugh Dickins <hughd@xxxxxxxxxx> Subject: mm: page_idle_get_page() does not need lru_lock 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 https://lore.kernel.org/lkml/20150504031722.GA2768@blaptop 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). Link: https://lkml.kernel.org/r/1604566549-62481-8-git-send-email-alex.shi@xxxxxxxxxxxxxxxxx Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx> Signed-off-by: Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx> Acked-by: "Huang, Ying" <ying.huang@xxxxxxxxx> Acked-by: Vlastimil Babka <vbabka@xxxxxxx> Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx> Cc: Minchan Kim <minchan@xxxxxxxxxx> Cc: Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx> Cc: Alexander Duyck <alexander.duyck@xxxxxxxxx> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> Cc: "Chen, Rong A" <rong.a.chen@xxxxxxxxx> Cc: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx> Cc: Jann Horn <jannh@xxxxxxxxxx> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Cc: Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> Cc: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx> Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxx> Cc: Mika Penttilä <mika.penttila@xxxxxxxxxxxx> Cc: Shakeel Butt <shakeelb@xxxxxxxxxx> Cc: Tejun Heo <tj@xxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Wei Yang <richard.weiyang@xxxxxxxxx> Cc: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/page_idle.c | 4 ---- 1 file changed, 4 deletions(-) --- a/mm/page_idle.c~mm-page_idle_get_page-does-not-need-lru_lock +++ a/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) || !get_page_unless_zero(page)) return NULL; - pgdat = page_pgdat(page); - spin_lock_irq(&pgdat->lru_lock); if (unlikely(!PageLRU(page))) { put_page(page); page = NULL; } - spin_unlock_irq(&pgdat->lru_lock); return page; } _
