On 04/04/16 16:01, Minchan Kim wrote: > On Mon, Apr 04, 2016 at 03:53:59PM +1000, Balbir Singh wrote: >> >> On 30/03/16 18:12, Minchan Kim wrote: >>> Procedure of page migration is as follows: >>> >>> First of all, it should isolate a page from LRU and try to >>> migrate the page. If it is successful, it releases the page >>> for freeing. Otherwise, it should put the page back to LRU >>> list. >>> >>> For LRU pages, we have used putback_lru_page for both freeing >>> and putback to LRU list. It's okay because put_page is aware of >>> LRU list so if it releases last refcount of the page, it removes >>> the page from LRU list. However, It makes unnecessary operations >>> (e.g., lru_cache_add, pagevec and flags operations. It would be >>> not significant but no worth to do) and harder to support new >>> non-lru page migration because put_page isn't aware of non-lru >>> page's data structure. >>> >>> To solve the problem, we can add new hook in put_page with >>> PageMovable flags check but it can increase overhead in >>> hot path and needs new locking scheme to stabilize the flag check >>> with put_page. >>> >>> So, this patch cleans it up to divide two semantic(ie, put and putback). >>> If migration is successful, use put_page instead of putback_lru_page and >>> use putback_lru_page only on failure. That makes code more readable >>> and doesn't add overhead in put_page. >> So effectively when we return from unmap_and_move() the page is either >> put_page or putback_lru_page() and the page is gone from under us. > I didn't get your point. > Could you elaborate it more what you want to say about this patch? I was just adding to my understanding of this change based on your changelog. My understanding is that we take the extra reference in isolate_lru_page() but by the time we return from unmap_and_move() we drop the extra reference Balbir Singh -- 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>