question about /proc/kcore

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question about /proc/kcore

Jamie Levy
Hello,

I know this list has been rather quiet for a while...  so I might as
well ask a question :-)

I've been trying to find some information on /proc/kcore and have not
been entirely successful.  I know is that it is an alias to memory,
that is in ELF format, and that can be used with gdb to debug the
kernel.  The `k' seems to imply that it is the kernel's memory, but
all documentation I've found states that it is the size of physical
memory plus 4KB (example below):

https://www.redhat.com/docs/manuals/enterprise/RHEL-4-Manual/en-US/Reference_Guide/s2-proc-kcore.html

This does not seem to be the case, however, when I do a listing in
/proc/kcore on my machine (F8) which has 2 GB of memory:

ls -lh /proc/kcore
-r-------- 1 root root 897M 2008-08-01 19:05 /proc/kcore

I have confirmed the same type of results on other machines to which I
have access.  I also do not seem to have the kcore.h file on my system
(and I have kernel-devel installed), since it is a zero byte file:

-rw-r--r-- 1 root root 0 2008-07-21 02:05
/usr/src/kernels/2.6.25.11-60.fc8-i686/include/config/proc/kcore.h

I am also aware of other tools that can be used to extract information
about kcore like the redhat crash utility:

http://people.redhat.com/anderson/

I am wondering why there is a discrepancy between the documentation
and the actual implementation of the /proc/kcore file?  I would also
like to know where I can find more detailed information about the
kcore file besides the usual description of what it is and how to use
it for debugging.

All the best,

-Jamie Levy

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Re: question about /proc/kcore

Astarta
Jamie Levy wrote:
> Hello,
>
> I know this list has been rather quiet for a while...  so I might as
> well ask a question :-)

Hello,

I really thought that this list is completely dead :-)

>
> This does not seem to be the case, however, when I do a listing in
> /proc/kcore on my machine (F8) which has 2 GB of memory:
>
> ls -lh /proc/kcore
> -r-------- 1 root root 897M 2008-08-01 19:05 /proc/kcore
>
> I have confirmed the same type of results on other machines to which I
> have access.  I also do not seem to have the kcore.h file on my system
> (and I have kernel-devel installed), since it is a zero byte file:
>
> -rw-r--r-- 1 root root 0 2008-07-21 02:05
> /usr/src/kernels/2.6.25.11-60.fc8-i686/include/config/proc/kcore.h
>


As far as I know, the size of kcore is equal not to the size of _all_
physical memory installed on the machine, but just to the amount of
memory accessible by kernel.
Your kernel seems to be compiled with HIGHMEM support, and if you do `ls
-l /proc/kcore` you see your LOWMEM size, the real memory that the
kernel uses. That the reason why the difference you mentioned comes.

Someone will correct me, if I'm wrong :)

>
> All the best,
>
> -Jamie Levy
>
> _______________________________________________
> Fedora-women-list mailing list
> [hidden email]
> https://www.redhat.com/mailman/listinfo/fedora-women-list


--
with best regards,
Fadeeva Marina.

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Re: question about /proc/kcore

Gayathri Swaminathan
Think Jamie is right.

I have observed behaviour were this file grows based on accessed memory (would this be kernel shared mem params?)

But it is definitely not just size of physical RAM+4KB on a machine.

gayathri

On Sat, Aug 2, 2008 at 3:54 PM, Astarta <[hidden email]> wrote:
Jamie Levy wrote:
Hello,

I know this list has been rather quiet for a while...  so I might as
well ask a question :-)

Hello,

I really thought that this list is completely dead :-)



This does not seem to be the case, however, when I do a listing in
/proc/kcore on my machine (F8) which has 2 GB of memory:

ls -lh /proc/kcore
-r-------- 1 root root 897M 2008-08-01 19:05 /proc/kcore

I have confirmed the same type of results on other machines to which I
have access.  I also do not seem to have the kcore.h file on my system
(and I have kernel-devel installed), since it is a zero byte file:

-rw-r--r-- 1 root root 0 2008-07-21 02:05
/usr/src/kernels/2.6.25.11-60.fc8-i686/include/config/proc/kcore.h



As far as I know, the size of kcore is equal not to the size of _all_ physical memory installed on the machine, but just to the amount of memory accessible by kernel.
Your kernel seems to be compiled with HIGHMEM support, and if you do `ls -l /proc/kcore` you see your LOWMEM size, the real memory that the kernel uses. That the reason why the difference you mentioned comes.

Someone will correct me, if I'm wrong :)



All the best,

-Jamie Levy

_______________________________________________
Fedora-women-list mailing list
[hidden email]
https://www.redhat.com/mailman/listinfo/fedora-women-list


--
with best regards,
Fadeeva Marina.


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[hidden email]
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--
Gayathri Swaminathan
gpgkey: 3EFB3D39
Volunteer, FDP

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Re: question about /proc/kcore

Jamie Levy
Thank you both for your responses.  I still have not figured this out,
but I appreciate your replies.  I wasn't sure if this list was still
around, but I thought I would try to liven it up with a question ;-)

All the best,

-Jamie



On Sat, Aug 2, 2008 at 5:58 PM, Gayathri Swaminathan
<[hidden email]> wrote:

> Think Jamie is right.
>
> I have observed behaviour were this file grows based on accessed memory
> (would this be kernel shared mem params?)
>
> But it is definitely not just size of physical RAM+4KB on a machine.
>
> gayathri
>
> On Sat, Aug 2, 2008 at 3:54 PM, Astarta <[hidden email]> wrote:
>>
>> Jamie Levy wrote:
>>>
>>> Hello,
>>>
>>> I know this list has been rather quiet for a while...  so I might as
>>> well ask a question :-)
>>
>> Hello,
>>
>> I really thought that this list is completely dead :-)
>>
>>>
>>> This does not seem to be the case, however, when I do a listing in
>>> /proc/kcore on my machine (F8) which has 2 GB of memory:
>>>
>>> ls -lh /proc/kcore
>>> -r-------- 1 root root 897M 2008-08-01 19:05 /proc/kcore
>>>
>>> I have confirmed the same type of results on other machines to which I
>>> have access.  I also do not seem to have the kcore.h file on my system
>>> (and I have kernel-devel installed), since it is a zero byte file:
>>>
>>> -rw-r--r-- 1 root root 0 2008-07-21 02:05
>>> /usr/src/kernels/2.6.25.11-60.fc8-i686/include/config/proc/kcore.h
>>>
>>
>>
>> As far as I know, the size of kcore is equal not to the size of _all_
>> physical memory installed on the machine, but just to the amount of memory
>> accessible by kernel.
>> Your kernel seems to be compiled with HIGHMEM support, and if you do `ls
>> -l /proc/kcore` you see your LOWMEM size, the real memory that the kernel
>> uses. That the reason why the difference you mentioned comes.
>>
>> Someone will correct me, if I'm wrong :)
>>
>>>
>>> All the best,
>>>
>>> -Jamie Levy
>>>
>>> _______________________________________________
>>> Fedora-women-list mailing list
>>> [hidden email]
>>> https://www.redhat.com/mailman/listinfo/fedora-women-list
>>
>>
>> --
>> with best regards,
>> Fadeeva Marina.
>>
>> _______________________________________________
>> Fedora-women-list mailing list
>> [hidden email]
>> https://www.redhat.com/mailman/listinfo/fedora-women-list
>
>
>
> --
> Gayathri Swaminathan
> gpgkey: 3EFB3D39
> Volunteer, FDP
>



--
==============================
 Jamie Levy
 Computer Science Dept
 Queens College
 http://venus.cs.qc.edu/~jlevy
==============================

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Re: question about /proc/kcore

Gayathri Swaminathan
And, thanks for bringing it to life!

There are many RHEL-ish issues/resolutions that I encounter as well.

Will start sharing them here on :)

On Sun, Aug 3, 2008 at 9:31 PM, Jamie Levy <[hidden email]> wrote:
Thank you both for your responses.  I still have not figured this out,
but I appreciate your replies.  I wasn't sure if this list was still
around, but I thought I would try to liven it up with a question ;-)

All the best,

-Jamie


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[hidden email]
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