mips pmap patch

[Jayachandran C.]

On Thu, Aug 16, 2012 at 10:10 PM, Alan Cox <alc at rice.edu> wrote:
> On 08/15/2012 17:21, Jayachandran C. wrote:
>>
>> On Tue, Aug 14, 2012 at 1:58 AM, Alan Cox<alc at rice.edu>  wrote:
>>>
>>> On 08/13/2012 11:37, Jayachandran C. wrote:
[...]
>>>> I could not test for more than an hour on 32-bit due to another
>>>> problem (freelist 1 containing direct-mapped pages runs out of pages
>>>> after about an hour of compile test).  This issue has been there for a
>>>> long time, I am planning to look at it when I get a chance.
>>>>
>>> What exactly happens?  panic?  deadlock?
>>
>> The build slows down to a crawl and hangs when it runs out of pages in
>> the freelist.
>
>
> I'd like to see the output of "sysctl vm.phys_segs" and "sysctl
> vm.phys_free" from this machine.  Even better would be running "sysctl
> vm.phys_free" every 60 seconds during the buildworld.  Finally, I'd like to
> know whether or not either "ps" or "top" shows any threads blocked on the
> "swwrt" wait channel once things slow to a crawl.

I spent some time looking at this issue.  I use a very large kernel
image with built-in root filesystem, and this takes about 120 MB  out
of the direct mapped area. The remaining pages (~64 MB) are not enough
for the build process.  If I increase free memory in this area either
by reducing the rootfs size of by adding a few more memory segments to
this area, the build goes through fine.

I also found that when the build slows down, most of the pages taken
from freelist 1 are allocated by the UMA subsystem, which seems to
keep quite a few pages allocated.

Regards,
JC.