On Fri, 3 Nov 2017, Michal Hocko wrote: > On Fri 03-11-17 00:46:18, Hugh Dickins wrote: > > > > NAK. shmem_wait_for_pins() is waiting for temporary pins on the pages > > to go away, and using lru_add_drain_all() in the usual way, to lower > > the refcount of pages temporarily pinned in a pagevec somewhere. Page > > count is touched by draining pagevecs: I'm surprised to see you say > > that it isn't - or have pagevec page references been eliminated by > > a recent commit that I missed? > > I must be missing something here. __pagevec_lru_add_fn merely about > moving the page into the appropriate LRU list, pagevec_move_tail only > rotates, lru_deactivate_file_fn moves from active to inactive LRUs, > lru_lazyfree_fn moves from anon to file LRUs and activate_page_drain > just moves to the active list. None of those operations touch the page > count AFAICS. So I would agree that some pages might be pinned outside > of the LRU (lru_add_pvec) and thus unreclaimable but does this really > matter. Or what else I am missing? Line 213 of mm/swap.c? Where pagevec_lru_move_fn() calls release_pages() to release the extra references (which each page came in with when added). Think about it, the mayhem that would follow from a page being freed while on pagevec: of course it must hold a reference. The only surprise is that the extra reference is not needed while on LRU: one can think of PageLRU as an extension of the page count. Hugh -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
