On Thu, Nov 5, 2020 at 4:56 PM Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx> wrote: > > From: Hugh Dickins <hughd@xxxxxxxxxx> > > 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). > > Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx> > Signed-off-by: Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx> > Cc: Vlastimil Babka <vbabka@xxxxxxx> > Cc: Minchan Kim <minchan@xxxxxxxxxx> > Cc: Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx> > Cc: linux-mm@xxxxxxxxx > Cc: linux-kernel@xxxxxxxxxxxxxxx > --- > 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) || > !get_page_unless_zero(page)) > return NULL; > > - pgdat = page_pgdat(page); > - spin_lock_irq(&pgdat->lru_lock); get_page_unless_zero() is a full memory barrier. But do we need a compiler barrier here to prevent the compiler to cache PageLRU() results here? Otherwise looks OK to me, Acked-by: "Huang, Ying" <ying.huang@xxxxxxxxx> Best Regards, Huang, Ying > if (unlikely(!PageLRU(page))) { > put_page(page); > page = NULL; > } > - spin_unlock_irq(&pgdat->lru_lock); > return page; > } > > -- > 1.8.3.1 > >
