Hi Luiz, Thanks for your email! On Fri, Nov 30, 2012 at 03:47:25PM -0200, Luiz Capitulino wrote: [...] > > But there is one, rather major issue: we're crossing kernel-userspace > > boundary. And with the scheme we'll have to cross the boundary four times: > > query / reply-available / control / reply-shrunk / (and repeat if > > necessary, every SHRINK_BATCH pages). Plus, it has to be done somewhat > > synchronously (all the four stages), and/or we have to make a "userspace > > shrinker" thread working in parallel with the normal shrinker, and here, > > I'm afraid, we'll see more strange interactions. :) > > Wouldn't this be just like kswapd? Sure, this is similar, but only for indirect reclaim (obviously). How we'd do this for the direct reclaim I have no idea, honestly, with Andrew's idea it must be all synchronous, so playing ping-pong with userland during the direct reclaim will be hard. So, the best thing to do with the direct recaim, IMHO, is just send a notification. > > But there is a good news: for these kind of fine-grained control we have a > > better interface, where we don't have to communicate [very often] w/ the > > kernel. These are "volatile ranges", where userland itself marks chunks of > > data as "I might need it, but I won't cry if you recycle it; but when I > > access it next time, let me know if you actually recycled it". Yes, > > userland no longer able to decide which exact page it permits to recycle, > > but we don't have use-cases when we actually care that much. And if we do, > > we'd rather introduce volatile LRUs with different priorities, or > > something alike. > > I'm new to this stuff so please take this with a grain of salt, but I'm > not sure volatile ranges would be a good fit for our use case: we want to > make (kvm) guests reduce their memory when the host is getting memory > pressure. Yes, for this kind of things you want a simple notification. I wasn't saying that volatile ranges must be a substitute for notifications, quite the opposite: I was saying that you can do volatile ranges in userland by using "userland-shrinker". It can be even wrapped into a library, with the same mmap() libc interface. But it will be inefficient. Thanks, Anton. -- 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>