Date: Tue, 6 Dec 2011 00:34:23 -0500 From: Arnaud Lacombe <lacombar@gmail.com> To: alc@freebsd.org Cc: freebsd-stable <freebsd-stable@freebsd.org> Subject: Re: PAE broken on 7-STABLE Message-ID: <CACqU3MW5w2dsng-cmEWVa5=NJM_DKseKaLTjdS1ALwPFT4gs%2BQ@mail.gmail.com> In-Reply-To: <CAJUyCcPRCndT%2B8RuSrC64kbJPUhFA0f9bCvGNcmbajstkX8CRg@mail.gmail.com> References: <CACqU3MXqSG5PUY_iVFmk8agV0qnHqtZqqi1Qn7LT6Lrp1DTH2w@mail.gmail.com> <CAJUyCcPRCndT%2B8RuSrC64kbJPUhFA0f9bCvGNcmbajstkX8CRg@mail.gmail.com>
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Hi, On Mon, Dec 5, 2011 at 10:02 PM, Alan Cox <alan.l.cox@gmail.com> wrote: > On Mon, Dec 5, 2011 at 4:15 PM, Arnaud Lacombe <lacombar@gmail.com> wrote: >> >> Hi, >> >> A FreeBSD 7-STABLE miserably crashes on the following: >> >> Fatal trap 12: page fault while in kernel mode >> cpuid = 0; apic id = 00 >> fault virtual address = 0xbfef0000 >> fault code = supervisor read, page not present >> instruction pointer = 0x20:0xc05fd1c2 >> stack pointer = 0x28:0xc0af6c7c >> frame pointer = 0x28:0xc0af6cc0 >> code segment = base 0x0, limit 0xfffff, type 0x1b >> = DPL 0, pres 1, def32 1, gran 1 >> processor eflags = interrupt enabled, resume, IOPL = 0 >> current process = 0 () >> trap number = 12 >> panic: page fault >> cpuid = 0 >> KDB: stack >> backtrace: >> db_trace_self_wrapper(c0662728,0,c062b78b,c0af6b28,0,...) at >> db_trace_self_wrapper+0x26panic(c062b78b,c06639cc,c06c1de4,1,1,...) at >> panic+0x106trap_fatal(c0c74388,c065b897,c064d922,10,c0c74000,...) at >> trap_fatal+0x270 >> trap_pfault(c06d4e40,c0c74380,c0af6c40,3,c06c1bc0,...) at >> trap_pfault+0x2aa >> trap(c0af6c3c) at trap+0x36ecalltrap() at calltrap+0x6 >> --- trap 0xc, eip = 0xc05fd1c2, esp = 0xc0af6c7c, ebp = 0xc0af6cc0 --- >> pmap_map(c0af6d68,3f6ba000,6,3fef8000,6,...) at pmap_map+0x72 >> vm_page_startup(c0d3e000,a,c0af6d88,c03f8f26,0,...) at >> vm_page_startup+0x35a >> vm_mem_init(0,af0000,af0020,af0000,0,...) at vm_mem_init+0x18 >> mi_startup() at mi_startup+0x56begin() at begin+0x2c >> >> on a machine with 24GB of RAM, while PAE is meant to support up to 64GB. >> >> - Arnaud >> >> ps: this is just a report, I'm not really expecting anything, any >> longer, from the FreebSD "community". >> > > At this early stage in the boot process, the page table pages for the kernel > address space must be statically allocated. When PAE was still actively > used, it was unusual to find machines that had more than about 16GB of RAM. > So, the static allocation of page table pages was set accordingly. For > larger machines, it is necessary to increase NKPT. The following comment > appears in i386/include/pmap.h: > > /* Initial number of kernel page tables. */ > #ifndef NKPT > #ifdef PAE > /* 152 page tables needed to map 16G (76B "struct vm_page", 2M page tables). > */ > #define NKPT 240 > #else > /* 18 page tables needed to map 4G (72B "struct vm_page", 4M page tables). > */ > #define NKPT 30 > #endif > #endif > > That said, a machine with 24GB of RAM is likely not going to be usable for > many workloads unless you also increase the size of the kernel virtual > address space (and thereby reduce the size of the user virtual address > space). > btw, thanks for the precise explanation! - Arnaud
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