On Wed, Mar 01, 2017 at 06:49:56PM +0100, Michal Hocko wrote: > On Wed 01-03-17 09:37:10, Shaohua Li wrote: > > On Wed, Mar 01, 2017 at 02:36:24PM +0100, Michal Hocko wrote: > > > On Fri 24-02-17 13:31:49, Shaohua Li wrote: > > > > show MADV_FREE pages info of each vma in smaps. The interface is for > > > > diganose or monitoring purpose, userspace could use it to understand > > > > what happens in the application. Since userspace could dirty MADV_FREE > > > > pages without notice from kernel, this interface is the only place we > > > > can get accurate accounting info about MADV_FREE pages. > > > > > > I have just got to test this patchset and noticed something that was a > > > bit surprising > > > > > > madvise(mmap(len), len, MADV_FREE) > > > Size: 102400 kB > > > Rss: 102400 kB > > > Pss: 102400 kB > > > Shared_Clean: 0 kB > > > Shared_Dirty: 0 kB > > > Private_Clean: 102400 kB > > > Private_Dirty: 0 kB > > > Referenced: 0 kB > > > Anonymous: 102400 kB > > > LazyFree: 102368 kB > > > > > > It took me a some time to realize that LazyFree is not accurate because > > > there are still pages on the per-cpu lru_lazyfree_pvecs. I believe this > > > is an implementation detail which shouldn't be visible to the userspace. > > > Should we simply drain the pagevec? A crude way would be to simply > > > lru_add_drain_all after we are done with the given range. We can also > > > make this lru_lazyfree_pvecs specific but I am not sure this is worth > > > the additional code. > > > > Minchan's original patch includes a drain of pvec. I discard it because I think > > it's not worth the effort. There aren't too many memory in the per-cpu vecs. > > but multiply that by the number of CPUs. > > > Like what you said, I doubt this is noticeable to userspace. > > maybe I wasn't clear enough. I've noticed and I expect others would as > well. We really shouldn't leak implementation details like that. So I > _believe_ this should be fixed. Draining all pagevecs is rather coarse > but it is the simplest thing to do. If you do not want to fold this > into the original patch I can send a standalone one. Or do you have any > concerns about draining? No, no objection at all. Just doubt it's worthy. Looks nobody complains similar issue, For exmaple, deactivate_file_page does the similar thing, then the smaps 'Referenced' could be inaccurate. Thanks, Shaohua -- 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>
