On Mon, Oct 31, 2011 at 09:10:49AM +0800, Shaohua Li wrote: > On Fri, 2011-10-28 at 17:50 +0800, Minchan Kim wrote: > > On Fri, Oct 28, 2011 at 04:25:56PM +0800, Shaohua Li wrote: > > > On Fri, 2011-10-28 at 15:30 +0800, Minchan Kim wrote: > > > > On Fri, Oct 28, 2011 at 01:11:55PM +0800, Shaohua Li wrote: > > > > > On Fri, 2011-10-28 at 07:34 +0800, Minchan Kim wrote: > > > > > > On Tue, Oct 25, 2011 at 10:59:40AM +0800, Shaohua Li wrote: > > > > > > > With current logic, if page reclaim finds a huge page, it will just reclaim > > > > > > > the head page and leave tail pages reclaimed later. Let's take an example, > > > > > > > lru list has page A and B, page A is huge page: > > > > > > > 1. page A is isolated > > > > > > > 2. page B is isolated > > > > > > > 3. shrink_page_list() adds page A to swap page cache. so page A is split. > > > > > > > page A+1, page A+2, ... are added to lru list. > > > > > > > 4. shrink_page_list() adds page B to swap page cache. > > > > > > > 5. page A and B is written out and reclaimed. > > > > > > > 6. page A+1, A+2 ... is isolated and reclaimed later. > > > > > > > So the reclaim order is A, B, ...(maybe other pages), A+1, A+2 ... > > > > > > > > > > > > I don't see your code yet but have a question. > > > > > > You mitigate this problem by 4/5 which could add subpages into lru tail > > > > > > so subpages would reclaim next interation of reclaim. > > > > > > > > > > > > What do we need 5/5? > > > > > > Do I miss something? > > > > > Both patches are required. without this patch, current page reclaim will > > > > > only reclaim the first page of a huge page, because the hugepage isn't > > > > > split yet. The hugepage is split when the first page is being written to > > > > > swap, which is too later and page reclaim might already isolated a lot > > > > > of pages. > > > > > > > > When split happens, subpages would be located in tail of LRU by your 4/5. > > > > (Assume tail of LRU is old age). > > > yes, but a lot of other pages already isolated. we will reclaim those > > > pages first. for example, reclaim huge page A, B. current reclaim order > > > is A, B, A+1, ... B+1, because we will isolated A and B first, all tail > > > pages are not isolated yet. While with my patch, the order is A, A > > > +1, ... B, B+1,.... with my patch, we can avoid unnecessary page split > > > or page isolation. This is exactly why my patch reduces the thp_split > > > count. > > > > It's possbile but I doubt how it is effective becuase add_to_swap has a unlikely as follows > > > > if (unlikely(PageTransHuge(page))) > > > > I don't mean unlikely assumption is absolutely right. > > But at least, you have to convince us of it's wrong. > > Personally, I don't want to add more logic and handling THP pages > > different with normal page unless it's real concern. > if you actually use THP, you will find it's a problem. The data I posted > already clearly showed it. > If so, could you fix above thing in next iteration if you don't mind? Thanks. -- Kind regards, Minchan Kim -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>