Date: Mon, 20 Aug 2012 10:54:43 -0500 From: Alan Cox <alc@rice.edu> To: "Jayachandran C." <c.jayachandran@gmail.com> Cc: mips@freebsd.org Subject: Re: mips pmap patch Message-ID: <50325DC3.3090201@rice.edu> In-Reply-To: <CA%2B7sy7CK=EXu88XKYYXDV1uf3U7eebq3e6rfwgHRhQyFTMv7dQ@mail.gmail.com> 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> <CA%2B7sy7CK=EXu88XKYYXDV1uf3U7eebq3e6rfwgHRhQyFTMv7dQ@mail.gmail.com>
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On 08/20/2012 05:36, Jayachandran C. wrote: > 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'm still curious to see what "sysctl vm.phys_segs" says. It sounds like roughly half of the direct map region is going to DRAM and half to memory-mapped I/O devices. Is that correct? > 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. At worst, it may be necessary to disable the use of uma_small_alloc() for this machine configuration. At best, uma_small_alloc() could be revised opportunistically use pages in the direct map region, but have the ability to fall back to pages that have to be mapped. Alan
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