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: 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.

-- 
Thanks,
Zhouping

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