From: Michal Hocko <mhocko@kernel.org>
To: Qian Cai <cai@lca.pw>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Waiman Long <longman@redhat.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Johannes Weiner <hannes@cmpxchg.org>,
Roman Gushchin <guro@fb.com>, Vlastimil Babka <vbabka@suse.cz>,
Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
Jann Horn <jannh@google.com>, Song Liu <songliubraving@fb.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Rafael Aquini <aquini@redhat.com>
Subject: Re: [PATCH] mm/vmstat: Reduce zone lock hold time when reading /proc/pagetypeinfo
Date: Thu, 24 Oct 2019 09:42:05 +0200 [thread overview]
Message-ID: <20191024074205.GQ17610@dhcp22.suse.cz> (raw)
In-Reply-To: <4D23D83F-190F-40B3-9EB9-C167642321B2@lca.pw>
On Thu 24-10-19 01:33:01, Qian Cai wrote:
>
>
> > On Oct 23, 2019, at 6:30 PM, Andrew Morton <akpm@linux-foundation.org> wrote:
> >
> > Yes, removing things is hard. One approach is to add printk_once(this
> > is going away, please email us if you use it) then wait a few years.
> > Backport that one-liner into -stable kernels to hopefully speed up the
> > process.
>
> Although it still look like an overkill to me given,
>
> 1) Mel given a green light to remove it.
> 2) Nobody justifies any sensible reason to keep it apart from it was
> probably only triggering by some testing tools blindly read procfs
> entries.
It's been useful for debugging memory fragmentation problems and we do
not have anything that would provide a similar information. Considering
that making it root only is trivial and reducing the lock hold times
likewise I do not really see any strong reason to dump it at this
moment.
> it is still better than wasting developers’ time to beating the “dead” horse.
>
> >
> > Meanwhile, we need to fix the DoS opportunity. How about my suggestion
> > that we limit the count to 1024, see if anyone notices? I bet they
> > don't!
>
> The DoS is probably there since the file had been introduced almost 10
> years ago, so I suspect it is not that easily exploitable.
Yes you need _tons_ of memory. Reading the file on my 3TB system takes
sys 0m3.673s
The situation might be worse if the system is terribly fragmented which
is not the case here.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2019-10-24 7:42 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-22 16:21 Waiman Long
2019-10-22 16:57 ` Michal Hocko
2019-10-22 18:00 ` Waiman Long
2019-10-22 18:40 ` Waiman Long
2019-10-23 0:52 ` David Rientjes
2019-10-23 8:31 ` Mel Gorman
2019-10-23 9:04 ` Michal Hocko
2019-10-23 9:56 ` Mel Gorman
2019-10-23 10:27 ` [RFC PATCH 0/2] " Michal Hocko
2019-10-23 10:27 ` [RFC PATCH 1/2] mm, vmstat: hide /proc/pagetypeinfo from normal users Michal Hocko
2019-10-23 13:13 ` Mel Gorman
2019-10-23 13:27 ` Vlastimil Babka
2019-10-23 14:52 ` Waiman Long
2019-10-23 15:10 ` Rafael Aquini
2019-10-23 16:15 ` Vlastimil Babka
2019-10-24 19:01 ` David Rientjes
2019-10-23 10:27 ` [RFC PATCH 2/2] mm, vmstat: reduce zone->lock holding time by /proc/pagetypeinfo Michal Hocko
2019-10-23 13:15 ` Mel Gorman
2019-10-23 13:32 ` Vlastimil Babka
2019-10-23 13:37 ` Michal Hocko
2019-10-23 13:48 ` Vlastimil Babka
2019-10-23 14:31 ` Michal Hocko
2019-10-23 16:20 ` Vlastimil Babka
2019-10-23 13:46 ` Rafael Aquini
2019-10-23 14:56 ` Waiman Long
2019-10-23 15:21 ` Waiman Long
2019-10-23 16:10 ` Michal Hocko
2019-10-23 16:17 ` Waiman Long
2019-10-23 16:21 ` Waiman Long
2019-10-23 16:15 ` Vlastimil Babka
2019-10-23 16:41 ` Michal Hocko
2019-10-23 16:47 ` Waiman Long
2019-10-23 17:34 ` [PATCH 1/2] mm, vmstat: Release zone lock more frequently when reading /proc/pagetypeinfo Waiman Long
2019-10-23 18:01 ` Michal Hocko
2019-10-23 18:14 ` Waiman Long
2019-10-23 20:02 ` Michal Hocko
2019-10-23 17:34 ` [PATCH 2/2] mm, vmstat: List total free blocks for each order in /proc/pagetypeinfo Waiman Long
2019-10-23 18:02 ` Michal Hocko
2019-10-23 18:07 ` Waiman Long
2019-10-24 8:20 ` [RFC PATCH 0/2] mm/vmstat: Reduce zone lock hold time when reading /proc/pagetypeinfo Michal Hocko
2019-10-24 16:16 ` Waiman Long
2019-10-23 12:42 ` [PATCH] " Qian Cai
2019-10-23 13:25 ` Vlastimil Babka
2019-10-22 21:59 ` Andrew Morton
2019-10-23 6:15 ` Michal Hocko
2019-10-23 14:30 ` Waiman Long
2019-10-23 14:48 ` Qian Cai
2019-10-23 15:01 ` Waiman Long
2019-10-23 15:05 ` Qian Cai
2019-10-23 22:30 ` Andrew Morton
2019-10-24 5:33 ` Qian Cai
2019-10-24 7:42 ` Michal Hocko [this message]
2019-10-24 11:11 ` Qian Cai
2019-10-24 13:38 ` Michal Hocko
2019-10-24 14:55 ` Qian Cai
2019-10-24 3:33 ` Feng Tang
2019-10-24 4:34 ` Qian Cai
2019-10-24 5:34 ` Feng Tang
2019-10-24 10:51 ` Qian Cai
2019-10-25 1:38 ` Feng Tang
2019-10-23 15:03 ` Rafael Aquini
2019-10-23 15:51 ` Qian Cai
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