On Thu, Oct 29, 2020 at 06:44:53PM +0800, Alex Shi 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(), That doesn't seem to be the case in Linus's or Andrew's tree. Am I missing a dependent patch series? > 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). Isn't it possible, as per Minchan's description, for page->mapping to point to a struct anon_vma without PAGE_MAPPING_ANON set, and rmap thinking it's looking at a struct address_space?
