mbuf autotuning effect

[Adrian Chadd]

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?


-adrian



On 6 September 2013 16:36, hiren panchasara <hiren.panchasara at 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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