Date: Thu, 12 Jul 2012 21:20:54 -0700 From: mdf@FreeBSD.org To: Justin Hibbits <chmeeedalf@gmail.com> Cc: freebsd-current <freebsd-current@freebsd.org>, FreeBSD PowerPC ML <freebsd-ppc@freebsd.org> Subject: Re: panic with DEBUG_MEMGUARD on PowerPC Message-ID: <CAMBSHm-CM0hc2Cu=C-zf7ArENqVz9iOHCjb0wMSPCnYQbXKqdA@mail.gmail.com> In-Reply-To: <307005B6-C8E5-4DCF-BD10-6BC79D8C2FE3@gmail.com> References: <A3CD63CD-694A-48F5-B0F7-9C8923AFCB90@gmail.com> <CAMBSHm-5Xix46MaYAwBek6hWvcOHZ7%2BR_4cpdG5SH_5RD7difQ@mail.gmail.com> <307005B6-C8E5-4DCF-BD10-6BC79D8C2FE3@gmail.com>
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On Thu, Jul 12, 2012 at 6:33 PM, Justin Hibbits <chmeeedalf@gmail.com> wrote: > On Jul 12, 2012, at 9:11 PM, mdf@freebsd.org wrote: > >> On Thu, Jul 12, 2012 at 4:43 PM, Justin Hibbits <chmeeedalf@gmail.com> >> wrote: >>> >>> When tracking down a panic exposed by INVARIANTS, I tried setting >>> DEBUG_MEMGUARD, so I could find the culprit that's trashing freed memory. >>> However, this causes a panic at bootup. It shows up right after the >>> first >>> WARNING: WITNESS message, with the following: >>> >>> Tracing, and printf() debugging, I see arguments to vm_map_findspace(): >>> start: 0xD0000000, length: 4246446080, and map->max_offset = 4026531839. >>> >>> Beyond that, I'm lost with tracking this down. Machine is a dual >>> processor >>> PowerPC G4, with 2GB RAM. >> >> >> The length is 0xFD1BA000 which is almost 4GB. Asking for 4GB of >> virtual space for 2GB of RAM sounds about right (it's been a while >> since I was in this code), unless this is a 32-bit kernel, in which >> case it'd be too much since there isn't that much virtual space >> available. >> >> So, is the kernel 32-bit? What are the values used and returned by >> memguard_fudge()? The intent of that routine is to get kmeminit() to >> allocate a larger map so memguard can use part of it for private >> virtual addresses. But it shouldn't be asking for "too much"; i.e. >> the intent was to check both physical and virtual space available and >> be greedy, but not too greedy. >> >> There were some issues with that code for some platforms that e.g. >> didn't define a VM_KMEM_SIZE_MAX, but alc@ fixed that in r216425. > > It is a 32-bit kernel, on 32-bit hardware. The values for memguard_fudge > are (defaults): > > tmp: 4246446080, vm_kmem_size: 117440512, vm_kmem_size_max: 0 > > When setting vm.kmem_size/vm.kmem_size_max to 2GB they are: > > tmp: 2147483648, vm_kmem_size: 214793648, vm_kmem_sizee_max: 2147483648 (all > 2GB). > > But the start and map->max_offset remain the same on all runs I make. memguard_fudge is still broken for 32-bit architectures with no vm_kmem_max. In the absence of a km_max to limit the value, we essentially use twice the physical memory for the virtual limit. But with 2GB on a 32-bit machine, this requires 4GB of virtual space. Setting vm_kmem_size_max to 2GB should work; I'd expect to see tmp=about 200MB, which is much larger than the input 112MB but the allocation should work. But I don't really know what else PowerPC has need of for virtual space, so that still could be too large. You can try smaller values of vm_kmem_size_max, like 1GB or 512MB. You shouldn't need to set vm_kmem_size at all. At some point the added space for the memguard_map will be small enough that the kmem_suballoc will work. Hmm, what is the min_offset and max_offset of kernel_map when the call to memguard_fudge is made? Thanks, matthew
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