svn commit: r243631 - in head/sys: kern sys

[Oleksandr Tymoshenko]

On 12/27/2012 6:46 PM, Oleksandr Tymoshenko wrote:
> On 12/18/2012 1:59 AM, Alan Cox wrote:
>> On 12/17/2012 23:40, Oleksandr Tymoshenko wrote:
>>> On 2012-12-08, at 1:21 PM, Alan Cox <alc at rice.edu> wrote:
>>>
>>>> On 12/08/2012 14:32, Andre Oppermann wrote:
>>> .. skipped ..
>>>
>>>>> The trouble seems to come from NSFBUFS which is (512 + maxusers * 16)
>>>>> resulting in a kernel map of (512 + 400 * 16) * PAGE_SIZE = 27MB.  
>>>>> This
>>>>> seem to be pushing it with the smaller ARM kmap layout.
>>>>>
>>>>> Does it boot and run when you set the tunable kern.ipc.nsfbufs=3500?
>>>>>
>>>>> ARM does have a direct map mode as well which doesn't require the
>>>>> allocation
>>>>> of sfbufs.  I'm not sure which other problems that approach has.
>>>>>
>>>> Only a few (3?) platforms use it.  It reduces the size of the user
>>>> address space, and translation between physical addresses and 
>>>> direct map
>>>> addresses is not computationally trivial as it is on other
>>>> architectures, e.g., amd64, ia64.  However, it does try to use large
>>>> page mappings.
>>>>
>>>>
>>>>> Hopefully alc@ (added to cc) can answer that and also why the kmap of
>>>>> 27MB
>>>>> manages to wrench the ARM kernel.
>>>>>
>>>> Arm does not define caps on either the buffer map size (param.h) or 
>>>> the
>>>> kmem map size (vmparam.h).  It would probably make sense to copy these
>>>> definitions from i386.
>>> Adding caps didn't help. I did some digging and found out that 
>>> although address range
>>> 0xc0000000 .. 0xffffffff is indeed valid for ARM in general actual 
>>> KVA space varies for
>>> each specific hardware platform. This "real" KVA is defined by 
>>> <virtual_avail, virtual_end>
>>> pair and ifI use them instead of <VM_MIN_KERNEL_ADDRESS, 
>>> VM_MAX_KERNEL_ADDRESS>
>>> in init_param2 function my pandaboard successfully boots. Since 
>>> former pair is used for defining
>>> kernel_map boundaries I believe it should be used for auto tuning as 
>>> well.
>>
>> That makes sense.  However, "virtual_avail" isn't the start of the
>> kernel address space.  The kernel map always starts at
>> VM_MIN_KERNEL_ADDRESS.  (See kmem_init().)  "virtual_avail" represents
>> the next unallocated virtual address in the kernel address space at an
>> early point in initialization.  "virtual_avail" and "virtual_end" aren't
>> used after that, or outside the VM system.  Please use
>> vm_map_min(kernel_map) and vm_map_max(kernel_map) instead.
>
> I checked: kernel_map is not available (NULL) at this point.  So we 
> can't use it to
> determine real KVA size. Closest thing we can get is 
> virtual_avail/virtual_end pair.
>
> Andre, could you approve attached patch for commit or suggest better 
> solution?

Any update on this one? Can I proceed with commit?