[Crash-utility] [PATCH] Add -m option to kmem

[Zhang Yanfei]

于 2013年03月28日 01:54, Dave Anderson 写道:
> 
> 
> ----- Original Message -----
>>
>>
>>
>> 在 2013年3月27日星期三，Dave Anderson 写道：
>>
>>
>>
>>
>> ----- Original Message -----
>>> kmem -m|-M is used for displaying information of all ksm pages or
>>> some ksm pages for specified ksm stable tree node addresses
>>>
>>> for example:
>>> crash> kmem -m
>>> STABLE_NODE : ffff88083fc927e0
>>> PAGE : ffffea000e667998
>>> PHYSICAL ADDRESS: 41d475000
>>>
>>> PID: 2967 MAPPING: 3
>>>
>>> STABLE_NODE : ffff88083fc84a10
>>> PAGE : ffffea000e3dd5d8
>>> PHYSICAL ADDRESS: 411aad000
>>>
>>> PID: 2967 MAPPING: 7
>>>
>>> STABLE_NODE : ffff88041980dda8
>>> PAGE : ffffea000e335568
>>> PHYSICAL ADDRESS: 40eaab000
>>>
>>> PID: 2967 MAPPING: 8
>>> ...
>>>
>>> STABLE_NODE : ffff880841ea43f8
>>> PAGE : ffffea000f62de38
>>> PHYSICAL ADDRESS: 465641000
>>>
>>> PID: 2967 MAPPING: 729
>>> PID: 3017 MAPPING: 499
>>>
>>> P.S.
>>> This patch is based on the patch from Qiao(qiaonuohan at cn.fujitsu.com )
>>> 0001-make-rbtree-manipulation-functions-global.patch
>>> Because this patch also uses rb_tree operations.
>>
>> I cannot test this because all of my sample dumps either return:
>>
>> crash> kmem -m
>> kmem: -m option not supported or applicable on this architecture or
>> kernel
>> crash>
>>
>> this is the kernel that doesn't support ksm
>>
>> or:
>>
>> crash> kmem -m
>> ksm may not be enabled
>> crash>
>>
>> This is because ksm is disabled or there is no ksm page in your
>> system.
> 
> Which one?  Can't you determine that?

I will change the message to:

no ksm pages in the system

meaning that there is not any ksm page in the system.

> 
>>
>> which, by the way, is not a very helpful error message.
>>
>> Do you have a reasonably-sized vmcore that I can download and test?
>>
>> I have no vmcore on hand now. You could follow the below steps to
>> make ksm work in your system.
>>
>>     * Ensure you are using kernel >= 2.6.31-0.94.rc4.fc12 and qemu-kvm >=0.10.92-4.fc12
>>     * Run two or more similar virtual machines
>>     * service ksm start
>>     * service ksmtuned start
>>     * Wait a while
>>     * Check whether pages were merged using /sys/kernel/mm/ksm/pages_shared
>>     * If value in /sys/kernel/mm/ksm/pages_shared is not zero, you
>>       could run crash kmem -m to see the output.
> 
> OK look, if I get the time, I'll try to set this up...  
> 
> But just the fact that I have to go to all this trouble, and the fact 
> that you don't even have a sample vmcore available again begs the question
> as to how useful -- or better put -- how often, this command would ever
> be utilized.

Sorry about this. I will make a vmcore and tell where you can download it later.

> 
> On the other hand, if you were to create a "ksm" extension module, then 
> I would be more than happy to post it with all of the others on the 
> extensions web page.
> 
>> Also, I have a question about the help message:
>>
>> crash> help kmem
>>
>> NAME
>> kmem - kernel memory
>>
>> SYNOPSIS
>> kmem [-f|-F|-p|-c|-C|-i|-s|-S|-v|-V|-n|-z|-o|-m|-M] [slab] [[-P]
>> address]
>> [-g [flags]
>>
>> DESCRIPTION
>> ... [ cut ] ...
>> -m displays information of ksm pages.
>> -M same as -m, but also dumps virtual addresses that mapping the
>> ksm pages.
>> ... [ cut ] ...
>> address when used with -m or -M, the address can be either a ksm stable
>> tree node address, a page's physical address, or a page pointer,
>> the information of the ksm page (if it is) is displayed.
>> ... [ cut ] ...
>>
>> Display information of ksm pages:
>>
>> crash> kmem -m ffff88086f22eec0 ffff8803573964c0
>> STABLE_NODE : ffff88083fc927e0
>> PAGE : ffffea000e667998
>> PHYSICAL ADDRESS: 41d475000
>>
>> PID: 2967 MAPPING: 3
>>
>> STABLE_NODE : ffff88083fc84a10
>> PAGE : ffffea000e3dd5d8
>> PHYSICAL ADDRESS: 411aad000
>>
>> PID: 2967 MAPPING: 7
>>
>> STABLE_NODE : ffff88041980dda8
>> PAGE : ffffea000e335568
>> PHYSICAL ADDRESS: 40eaab000
>>
>> PID: 2967 MAPPING: 8
>>
>> ......
>>
>> STABLE_NODE : ffff880841ea43f8
>> PAGE : ffffea000f62de38
>> PHYSICAL ADDRESS: 465641000
>>
>> PID: 2967 MAPPING: 729
>> PID: 3017 MAPPING: 499
>>
>> crash>
>>
>> Please tell me how the two address arguments ffff88086f22eec0 and
>> ffff8803573964c0 have any relationship to the subsequent display?
>>
>>
>> Sorry this is a mistake. The two addresses in the example are
>> redundant.
> 
> Well, they aren't "redundant", they just don't make any sense at all.
> I'm presuming that they don't belong there at all, and that you're
> just showing the output of "kmem -m" alone, correct?

Yes, you are right.

Thanks
Zhang