Hi, Matthew, Matthew Wilcox <willy@xxxxxxxxxxxxx> writes: > On Fri, Feb 28, 2020 at 11:38:16AM +0800, Huang, Ying wrote: >> MADV_FREE is a lazy free mechanism in Linux. According to the manpage >> of mavise(2), the semantics of MADV_FREE is, >> >> The application no longer requires the pages in the range specified >> by addr and len. The kernel can thus free these pages, but the >> freeing could be delayed until memory pressure occurs. ... >> >> Originally, the pages freed lazily by MADV_FREE will only be freed >> really by page reclaiming when there is memory pressure or when >> unmapping the address range. In addition to that, there's another >> opportunity to free these pages really, when we try to migrate them. >> >> The main value to do that is to avoid to create the new memory >> pressure immediately if possible. Instead, even if the pages are >> required again, they will be allocated gradually on demand. That is, >> the memory will be allocated lazily when necessary. This follows the >> common philosophy in the Linux kernel, allocate resources lazily on >> demand. > > Do you have an example program which does this (and so benefits)? Sorry, what do you mean exactly for "this" here? Call madvise(,,MADV_FREE)? Or migrate pages? > If so, can you quantify the benefit at all? The question is what is the right workload? For example, I can build a scenario as below to show benefit. - run program A in node 0 with many lazily freed pages - run program B in node 1, so that the free memory on node 1 is low - migrate the program A from node 0 to node 1, so that the program B is influenced by the memory pressure created by migrating lazily freed pages. Best Regards, Huang, Ying
