Re: maximum memory size allocated by _xmalloc

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 12/07/12 01:01, Chulmin Kim wrote:
>> On 11/07/12 10:13, Chulmin Kim wrote:
>>> Hi all,
>>>
>>> I'm currently inserting my own code to adjust the several existing
>>> memory ballooning works.
>>>
>>> To accomplish it, I manage some kind of statistics in Xen memory area.
>>>
>>> Using _xmalloc, I've allocated certain size of memory chunk for the
>>> data structure. ( I varied it from 10kb to 24 MB.)
>>>
>>> When the size is equal to 24 MB, xen won't boot anymore.  (stuck
>>> during the xmalloc, according to my debugging. _xmalloc returns NULL.)
>>> There was no problem when the size is below 12MB.
>>>
>>> Is there any limitation such as max memory size for _xmalloc?
>>>
>>> I suspected xen heap size, but, it is no longer adjustable. Right?
>>>
>>> I hope somebody can give me a clue.  Thanks.
>> _xmalloc will first try to use the size pools for allocation, and failing
> that, try to
>> allocate full pages.
>>
>> As it is returning NULL, this probably means you no longer have 24MB of
> free
>> contiguous RAM to allocate.
>>
>> ~Andrew
>>
> Thanks for the reply, Andrew.
>
> I have to check the contiguity. 
>
> If it is the cause of the problem, then, how can I detour this problem? 
>
> Other xen part calling xmalloc_array does not handle this problem as far as
> I know. (only consider it as an error)
>
> Should I split the data structure into two or more chunks? 

Personally, I would think that 24M is a stupidly large amount to be
trying to allocate with xmalloc and friends.

If you are using that much memory, it might be worth using
alloc_xenheap_pages() and working with full pages instead.

Why do you need so much space for memory statistics?

~Andrew

-- 
Andrew Cooper - Dom0 Kernel Engineer, Citrix XenServer
T: +44 (0)1223 225 900, http://www.citrix.com