lkml.org 
[lkml]   [2019]   [Oct]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] mm/vmstat: Reduce zone lock hold time when reading /proc/pagetypeinfo
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

\
 
 \ /
  Last update: 2019-10-24 09:43    [W:0.047 / U:1.216 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site