Date: Wed, 09 Jan 2008 11:13:22 +0100 From: Kris Kennaway <kris@FreeBSD.org> To: Joshua Isom <jrisom@gmail.com> Cc: freebsd-hackers@freebsd.org, Bharma Ji <bharmaji@gmail.com> Subject: Re: Graceful failure instead of panicking in kmem_malloc Message-ID: <47849E42.7090201@FreeBSD.org> In-Reply-To: <66462bcb31fb347796200bd5260d7cdc@gmail.com> References: <67beabb0801081555v4ca3b729x294322fa724afa09@mail.gmail.com> <4784159E.9040905@FreeBSD.org> <67beabb0801081925t67f995b8hc4cc779f88c2ba@mail.gmail.com> <66462bcb31fb347796200bd5260d7cdc@gmail.com>
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Joshua Isom wrote:
>
> 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@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.
This is kernel memory, not user memory. There is a fixed-size arena for
mallocs in the kernel, and the panic happens when it fills up and no
free space can be immediately reclaimed.
Kris
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