On Sep 6, 2013, at 7:11 PM, Adrian Chadd wrote:
> Yeah, why is VM_KMEM_SIZE only 12mbyte for MIPS? That's a little low for a
> platform that has a direct map that's slightly larger than 12mb :)
>
> Warner? Juli?
All architectures have it at 12MB, except sparc64 where it is 16MB. This can be
changed with the options VM_KMEM_SIZE=xxxxx in the config file.
So my guess as to why this is the case: cut and paste worked, so nobody changed
it after that.
# Still need to reads hiren's email to comprehend it...
Warner
>
>
> -adrian
>
>
>
> On 6 September 2013 16:36, hiren panchasara <hiren.panchas...@gmail.com>wrote:
>
>> We are seeing an interesting thing on a mips board with 32MB ram.
>>
>> We run out of mbuf very easily and looking at numbers it seems we are only
>> getting 6mb of maxmbufmem.
>>
>> # sysctl -a | grep hw | grep mem
>> hw.physmem: 33554432
>> hw.usermem: 21774336
>> hw.realmem: 33554432
>> #
>> # sysctl -a | grep maxmbuf
>> kern.ipc.maxmbufmem: 6291456
>>
>> I believe that number is very low for a board with 32mb of ram.
>>
>> Looking at the code:
>>
>> sys/kern/kern_mbuf.c : tunable_mbinit()
>>
>> 124 realmem = qmin((quad_t)physmem * PAGE_SIZE, vm_kmem_size);
>> 125 maxmbufmem = realmem / 2;
>> 126 TUNABLE_QUAD_FETCH("kern.ipc.maxmbufmem", &maxmbufmem);
>> 127 if (maxmbufmem > realmem / 4 * 3)
>> 128 maxmbufmem = realmem / 4 * 3;
>>
>> So, realmem plays important role in determining maxmbufmem.
>>
>> physmem = 32mb
>> PAGE_SIZE = 4096
>>
>> vm_kmem_size is calculated inside sys/kern/kern_malloc.c : kmeminit()
>>
>> 705 vm_kmem_size = VM_KMEM_SIZE + nmbclusters * PAGE_SIZE;
>> 706 mem_size = cnt.v_page_count;
>> 707
>> 708 #if defined(VM_KMEM_SIZE_SCALE)
>> 709 vm_kmem_size_scale = VM_KMEM_SIZE_SCALE;
>> 710 #endif
>> 711 TUNABLE_INT_FETCH("vm.kmem_size_scale", &vm_kmem_size_scale);
>> 712 if (vm_kmem_size_scale > 0 &&
>> 713 (mem_size / vm_kmem_size_scale) > (vm_kmem_size /
>> PAGE_SIZE))
>> 714 vm_kmem_size = (mem_size / vm_kmem_size_scale) *
>> PAGE_SIZE;
>>
>> here,
>> VM_KMEM_SIZE = 12*1024*1024
>> nmbclusters = 0 (initially)
>> PAGE_SIZE = 4096
>> # sysctl -a | grep v_page_count
>> vm.stats.vm.v_page_count: 7035
>>
>> and VM_KMEM_SIZE_SCALE = 3 for mips.
>>
>> So, vm_kmem_size = 12mb.
>>
>> Going back to tunable_mbinit(),
>> we get realmem = 12mb.
>> and masmbufmem = 6mb.
>>
>>
>> Wanted to see if I am following the code correctly and how autotuning
>> should work here.
>>
>> cheers,
>> Hiren
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