From: Shaohua Li <shli@fb.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Kernel-team@fb.com, minchan@kernel.org, hughd@google.com,
hannes@cmpxchg.org, riel@redhat.com, mgorman@techsingularity.net,
akpm@linux-foundation.org
Subject: Re: [PATCH V5 6/6] proc: show MADV_FREE pages info in smaps
Date: Wed, 1 Mar 2017 10:18:10 -0800 [thread overview]
Message-ID: <20170301181809.GA17275@shli-mbp.local> (raw)
In-Reply-To: <20170301174955.GB20360@dhcp22.suse.cz>
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
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next prev parent reply other threads:[~2017-03-01 18:18 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-24 21:31 [PATCH V5 0/6] mm: fix some MADV_FREE issues Shaohua Li
2017-02-24 21:31 ` [PATCH V5 1/6] mm: delete unnecessary TTU_* flags Shaohua Li
2017-02-27 13:48 ` Michal Hocko
2017-02-24 21:31 ` [PATCH V5 2/6] mm: don't assume anonymous pages have SwapBacked flag Shaohua Li
2017-02-27 6:48 ` Hillf Danton
2017-02-27 14:35 ` Michal Hocko
2017-02-27 16:10 ` Shaohua Li
2017-02-27 16:28 ` Michal Hocko
2017-02-24 21:31 ` [PATCH V5 3/6] mm: move MADV_FREE pages into LRU_INACTIVE_FILE list Shaohua Li
2017-02-27 6:28 ` Minchan Kim
2017-02-27 16:13 ` Shaohua Li
2017-02-27 16:30 ` Michal Hocko
2017-02-28 2:53 ` Minchan Kim
2017-02-27 14:53 ` Michal Hocko
2017-02-27 17:15 ` Johannes Weiner
2017-02-28 3:19 ` Hillf Danton
2017-02-24 21:31 ` [PATCH V5 4/6] mm: reclaim MADV_FREE pages Shaohua Li
2017-02-27 6:33 ` Minchan Kim
2017-02-27 16:19 ` Shaohua Li
2017-02-27 16:32 ` Michal Hocko
2017-02-28 5:02 ` Minchan Kim
2017-02-27 15:05 ` Michal Hocko
2017-02-27 17:21 ` Johannes Weiner
2017-02-28 3:21 ` Hillf Danton
2017-02-24 21:31 ` [PATCH V5 5/6] mm: enable MADV_FREE for swapless system Shaohua Li
2017-02-27 15:06 ` Michal Hocko
2017-02-28 3:22 ` Hillf Danton
2017-02-28 5:02 ` Minchan Kim
2017-02-24 21:31 ` [PATCH V5 6/6] proc: show MADV_FREE pages info in smaps Shaohua Li
2017-02-27 15:06 ` Michal Hocko
2017-02-28 3:23 ` Hillf Danton
2017-03-01 13:36 ` Michal Hocko
2017-03-01 17:37 ` Shaohua Li
2017-03-01 17:49 ` Michal Hocko
2017-03-01 18:18 ` Shaohua Li [this message]
2017-03-01 18:31 ` Johannes Weiner
2017-03-01 18:57 ` Michal Hocko
2017-03-02 7:39 ` Minchan Kim
2017-03-02 14:01 ` Johannes Weiner
2017-03-02 16:30 ` Michal Hocko
2017-03-04 0:10 ` Andrew Morton
2017-03-07 10:05 ` Michal Hocko
2017-03-07 22:43 ` Andrew Morton
2017-03-08 5:36 ` Minchan Kim
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