Re: [LTP] [PATCH] Set tunable value of min_free_kbytes lower

[Zhouping Liu <zliu@redhat.com>]

----- Original Message -----
> From: "Shuang Qiu" <shuang.qiu@oracle.com>
> To: "Zhouping Liu" <zliu@redhat.com>
> Cc: ltp-list@lists.sourceforge.net
> Sent: Monday, August 27, 2012 11:03:37 AM
> Subject: Re: [LTP] [PATCH] Set tunable value of min_free_kbytes lower
> 
> On 08/24/2012 09:48 PM, Zhouping Liu wrote:
> >
> > ----- Original Message -----
> >> From: "Shuang Qiu" <shuang.qiu@oracle.com>
> >> To: "Zhouping Liu" <zliu@redhat.com>
> >> Cc: ltp-list@lists.sourceforge.net
> >> Sent: Friday, August 24, 2012 6:18:00 PM
> >> Subject: Re: [LTP] [PATCH] Set tunable value of min_free_kbytes
> >> lower
> >>
> >> On 08/24/2012 04:11 PM, Zhouping Liu wrote:
> >>> ----- Original Message -----
> >>>> From: "shuang qiu" <shuang.qiu@oracle.com>
> >>>> To: ltp-list@lists.sourceforge.net
> >>>> Sent: Thursday, August 23, 2012 2:43:01 PM
> >>>> Subject: [LTP] [PATCH] Set tunable value of min_free_kbytes
> >>>> lower
> >>>>
> >>>> From: Shuang Qiu <shuang.qiu@oracle.com>
> >>>>
> >>>> The value of min_free_kbytes is set too high(half of mem_free)
> >>>> during
> >>>> testing min_free_kbytes tunable.It often cause the system to
> >>>> become
> >>>> out-of-memory.Using 20% of mem_free to avoid oom and system
> >>>> hang.
> >>> Hi, shuang
> >>>
> >>> I met the issue that min_free_kbytes caused system hang before,
> >>> and
> >>> what you said made sense.
> >>>
> >>> but after tested the patch, I found it still make the system hang
> >>> with the patch, so I don't think
> >>> this patch can fix the issue completely, maybe there are other
> >>> factors, or need lower tune value.
> >>> always suppose it was because of the high tune value, it's more
> >>> better to add an optional to control it.
> >>> also I will investigate it deeper to look after the real reason.
> >>> please comment if you have other ideas.
> >>>
> >>> Thanks,
> >>> Zhouping
> >> Thanks for testing,Zhouping.
> >>
> >> I find it says "However, setting this parameter to a value that is
> >> too
> >> high (5-10% of total system memory) will cause your system to
> >> become
> >> out-of-memory immediately." in redhat memory-tunables document.
> >> https://access.redhat.com/knowledge/docs/en-US/Red_Hat_Enterprise_Linux/6/html/Performance_Tuning_Guide/s-memory-tunables.html
> >> Set the value less than 5% of total memory will make it more safe.
> > Thanks for sharing this! I will take your ideas into account.
> >
> >> Let's think about a better option to control it.
> > Ok, I will prepare a patch for this.
> >
> >
> >> It is great that you will investigate it deeper.
> >> Seems there are some other problems in this case,it always failed
> >> with i386.
> >> The type of total_mem "unsigned long" is not suitable with
> >> nowadays
> >> memory ,it will overflow(with i386) in line 177:map_count =
> >> total_mem
> >> *
> >> KB / MAP_SIZE and the value of map_count is not correct.
> >> Using "unsigned long long" could fix this issue.
> >> But the case still failed after fix it.
> >> Could you help to investigate it too.
> > sure.
> >

Hi, Shuang

I think the below patch can't fix the issue, it looks more like a bug related to oom-killer,
I have opened a bug to trace it, please see https://bugzilla.redhat.com/show_bug.cgi?id=851938

> Hi Zhouping,
> I think the reason for the failures which I met is also that  it just
> catched oom_killer scenario when overcommit_memory=1.
> I found your patch before:
> commit 4f267b6fd11749c91211c9dbfc706cf46919650b
> Author: Zhouping Liu <zliu@redhat.com>
> Date:   Fri Mar 30 22:29:58 2012 +0800
> 
>      mm/tunable: fix unexpected error log in min_free_kbytes
> 
>      when overcommit_memory=0, mmap() will be destroyed in two below
> scenario:
>       1) MAP_FAILED with ENOMEM,
>       2) oom_killer kill it.
>      without the patch, it just catched oom_killer scenario,
>      the patch fixed it.
> 
> 
> Could this patch also for when overcommit_memory=1 scenario?
> 
> Thanks
> Shuang
> 
> 
> 

-- 
Thanks,
Zhouping

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