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. Like what you said, I doubt this is noticeable to userspace. Thanks, Shaohua > --- > diff --git a/mm/madvise.c b/mm/madvise.c > index dc5927c812d3..d2c318db16c9 100644 > --- a/mm/madvise.c > +++ b/mm/madvise.c > @@ -474,7 +474,7 @@ static int madvise_free_single_vma(struct vm_area_struct *vma, > madvise_free_page_range(&tlb, vma, start, end); > mmu_notifier_invalidate_range_end(mm, start, end); > tlb_finish_mmu(&tlb, start, end); > - > + lru_add_drain_all(); > return 0; > } > > -- > Michal Hocko > SUSE Labs -- 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>
