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Date:      Mon, 20 Aug 2012 16:06:56 +0530
From:      "Jayachandran C." <c.jayachandran@gmail.com>
To:        Alan Cox <alc@rice.edu>
Cc:        mips@freebsd.org
Subject:   Re: mips pmap patch
Message-ID:  <CA%2B7sy7CK=EXu88XKYYXDV1uf3U7eebq3e6rfwgHRhQyFTMv7dQ@mail.gmail.com>
In-Reply-To: <502D2271.6080105@rice.edu>
References:  <50228F5C.1000408@rice.edu> <CA%2B7sy7DxqhGhJt%2BwE3WW2-j4SxnPweULjYS5GQ=NgMYSrwJHtw@mail.gmail.com> <50269AD4.9050804@rice.edu> <CA%2B7sy7AZ-s2H6COfvz60N=kxw%2BWUiUC9diVfWg9aOzWSZKGWRQ@mail.gmail.com> <5029635A.4050209@rice.edu> <CA%2B7sy7Cnsy7Ag1iG=_Kj04gEXeYp7kZnpACQpD8THvkp0VKdcA@mail.gmail.com> <502D2271.6080105@rice.edu>

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On Thu, Aug 16, 2012 at 10:10 PM, Alan Cox <alc@rice.edu> wrote:
> On 08/15/2012 17:21, Jayachandran C. wrote:
>>
>> On Tue, Aug 14, 2012 at 1:58 AM, Alan Cox<alc@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.



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