[cfe-dev] Question about Clang/LLVM addresssanitizer

Kostya Serebryany via cfe-dev cfe-dev at lists.llvm.org
Thu Sep 22 13:30:18 PDT 2016


On Wed, Sep 21, 2016 at 10:12 PM, ZhaoKang <zhaokang at mail.tsinghua.edu.cn>
wrote:

> Hello James,
>
>
>
> Yes, the failed VM's 'cat /proc/sys/vm/overcommit_memory' is exactly 2,
> but the correct VM's is also 2. And I dump the memory and disk below:
>
>
>
> *Failed one*:
>
> fangqing@[xhdengvm155043 kcc_case]$ cat /proc/sys/vm/overcommit_memory
>
> 2
>
>
>
> fangqing@[xhdengvm155043 kcc_case]$ top
>
> top - 10:23:42 up 8 days, 11:12,  5 users,  load average: 0.07, 0.02, 0.00
>
> Tasks: 120 total,   1 running, 119 sleeping,   0 stopped,   0 zombie
>
> Cpu(s):  1.2%us,  0.0%sy,  0.0%ni, 98.8%id,  0.0%wa,  0.0%hi,  0.0%si,
> 0.0%st
>
> Mem:   5993176k total,  1598600k used,  4394576k free,   245492k buffers
>
> Swap:  4128760k total,        0k used,  4128760k free,   864412k cached
>
>
>
> fangqing@[xhdengvm155043 kcc_case]$ df -h .
>
> Filesystem            Size  Used Avail Use% Mounted on
>
> svmitfiler2-lif1:/Home/Home_xbj/fangqing
>
>                       6.2T  4.7T  1.5T  76% /home/Fangqing
>
>
>
> *Correct one*:
>
> fangqing@[xhdvdieodvm102 local]$ cat /proc/sys/vm/overcommit_memory
>
> 2
>
>
>
> fangqing@[xhdvdieodvm102 local]$ top
>
> top - 10:16:52 up 36 days, 21:47, 50 users,  load average: 2.51, 2.68, 2.70
>
> Tasks: 357 total,   4 running, 351 sleeping,   1 stopped,   1 zombie
>
> Cpu(s): 99.7%us,  0.3%sy,  0.0%ni,  0.0%id,  0.0%wa,  0.0%hi,  0.0%si,
> 0.0%st
>
> Mem:  16436116k total, 16347972k used,    88144k free,    38592k buffers
>
> Swap: 32767992k total,  2364888k used, 30403104k free, 14688384k cached
>
>
>
> fangqing@[xhdvdieodvm102 kcc_case]$ df -h .
>
> Filesystem            Size  Used Avail Use% Mounted on
>
> svmitfiler2-lif1:/Home/Home_xbj/fangqing
>
>                       6.2T  4.7T  1.5T  76% /home/Fangqing
>
>
>
> So why?
>
I frankly don't know.
On my box (Ubuntu 14.04) setting  /proc/sys/vm/overcommit_memory to 2 does
not cause the test to fail.
You should probably ask someone who knows more about the Linux Kernel.


> Thanks a lot!
>
> > -----原始邮件-----
> > 发件人: "James Knight" <jyknight at google.com>
> > 发送时间: 2016-09-22 11:23:07 (星期四)
> > 收件人: ZhaoKang <zhaokang at mail.tsinghua.edu.cn>, "ZhaoKang via cfe-dev" <
> cfe-dev at lists.llvm.org>
> > 抄送: "Kostya Serebryany" <kcc at google.com>
> > 主题: Re: [cfe-dev] Question about Clang/LLVM addresssanitizer
>
> >
> >
> > > On Sep 20, 2016, at 9:47 PM, ZhaoKang via cfe-dev <cfe-
> dev at lists.llvm.org> wrote:
> > >
> > > You mentioned that 'Some global settings in the system
> may for some reason reject such huge mappings.'
> > > And I want to know which kinds of settings may have this effect?
> >
> > cat /proc/sys/vm/overcommit_memory on your system.
> >
> > The default value is 0, which means allow overcommit
> heuristically when it seems likely to work.
> >
> > If, however, your system has that set to 2 (which I'm
> guessing it does), linux will ignore the MAP_NORESERVE flag,
>  and *always* demands you have enough ram and swap to
> hold everything that might ever possibly be written.
> >
> > In that case, either set it back to 0, or else add 16TB
> or so of swapspace to your system.
> >
> > Almost nobody ever sets that option to 2, because it'
> s almost completely useless to do so, and just breaks stuff. :)
>
>
>
>
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