Hi Bob, On Tue, Oct 11, 2011 at 05:24:26PM +0800, Bob Liu wrote: > Thanks for your reply. > > Yes, mlock() can do it but it will require a lot of changes in every > user application. > If some of the applications are hugh and complicated(even not opensource), it's > hard to modify them. > Add this patch can make things simple and thp more flexible. > > For using swapoff -a, it will disable swap for 4k normal pages. > > A simple use case is like this: > a lot of swap sensitive apps run on a machine, it will use thp so we > need to disable swap. > But this apps are hugh and complicated, it's hard to modify them by mlock(). > > In addition, there are also some normal and not swap sensitive apps > which don't use thp run on > the same machine, we can still reclaim their memory by swap when lack > of memory. I'm not convinced. If you need to disable swap selectively to certain apps but you can't modify them I'd suggest to add a mlock-equal-privileged prctl(PR_SWAP_ENABLE/DISABLE) that applies to all anonymous memory and tmpfs. Probably not to filebacked memory in case MAP_SHARED is used for all I/O. This seems too limited, it may happen to work well for a specific application but it's not generic enough. Another user could have a binary application with a ton of tmpfs shared memory that he can't modify (MAP_SHARED on /dev/zero for example) and he wants to mlock it but he can't. Or maybe another user has an application with <2M anonymous memory scattered in the middle of MAP_SHARED segments (so that can't be mapped by THP because of strict hardware limits) and he wants it to remain locked in ram too and not be swapped out for that specific app. So I prefer a solution that threats all anonymous memory and tmpfs memory equal (the only two entities in the kernel that will be paged out to swap). Or at the very least all anonymous memory equal... so it remains transparent as much as possible :). -- 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>