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.
---
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
