Graceful failure instead of panicking in kmem_malloc

[Joshua Isom]

On Jan 8, 2008, at 9:25 PM, Bharma Ji wrote:

> Thanks for the response. I am hoping to keep some memory aside  
> specifically
> for handling out of memory allocation situations. Yes the real fix is  
> to
> avoid out of memory allocation. Thanks for the patch. Will try that.  
> As a
> first cut I am just trying to handle failure gracefully.
>
> So asking again - if there is any way already discussed or  
> standardized to
> make the system handle failures gracefully
>
> On Jan 8, 2008 4:30 PM, Kris Kennaway <kris at freebsd.org> wrote:
>
>> Bharma Ji wrote:
>>> In FreeBSD 6_2, if kmem_malloc is unable to find space it panics. The
>>> relevant code is in vm_kern.c
>>>   if ((flags & M_NOWAIT) == 0)
>>>                          panic("kmem_malloc(%ld): kmem_map too small:
>> %ld
>>> total allocated",
>>>                                 (long)size, (long)map->size);
>>>
>>> Is there any way to make the system log and then gracefully shut off
>> instead
>>> of panicking?
>>
>> Not really, because those actions require memory allocation.  The real
>> fix is to either
>>
>> a) avoid running out of memory in the first place by tuning  
>> vm.kmem_size
>>
>> b) perhaps trying harder to avoid panicking by first trying to more
>> aggressively reclaim memory.
>>
>> You can try
>>
>>    
>> http://www.freebsd.org/~pjd/patches/vm_kern.c.2.patch<http:// 
>> www.freebsd.org/%7Epjd/patches/vm_kern.c.2.patch>
>>
>> which implements b) (patch against 7.0, but might apply to 6.2  
>> unchanged).
>>
>> Kris
>>
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Why not try to take out some user processes?  Going with a combination  
of process priority and memory usage, it should at least be more  
tolerable than a panic.