Date: Thu, 2 Dec 2010 17:47:27 +0100 From: Marius Strobl <marius@alchemy.franken.de> To: Alan Cox <alc@rice.edu> Cc: svn-src-head@freebsd.org, alc@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org, Max Khon <fjoe@samodelkin.net> Subject: Re: svn commit: r216016 - head/sys/sparc64/include Message-ID: <20101202164727.GB38282@alchemy.franken.de> In-Reply-To: <4CF691A5.8070608@rice.edu> References: <201011281926.oASJQKiE040689@svn.freebsd.org> <20101128194542.GF9966@alchemy.franken.de> <AANLkTinwkVO%2BRkr7coYGhuMdZ_UQQa3_18c3D6fBLucA@mail.gmail.com> <20101129192308.GX80343@alchemy.franken.de> <20101129192417.GA18893@alchemy.franken.de> <4CF691A5.8070608@rice.edu>
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On Wed, Dec 01, 2010 at 12:19:17PM -0600, Alan Cox wrote: > Marius Strobl wrote: > >On Mon, Nov 29, 2010 at 08:23:08PM +0100, Marius Strobl wrote: > > > >>On Tue, Nov 30, 2010 at 12:31:31AM +0600, Max Khon wrote: > >> > >>>Marius, > >>> > >>>On Mon, Nov 29, 2010 at 1:45 AM, Marius Strobl > >>><marius@alchemy.franken.de>wrote: > >>> > >>>On Sun, Nov 28, 2010 at 07:26:20PM +0000, Max Khon wrote: > >>> > >>>>>Author: fjoe > >>>>>Date: Sun Nov 28 19:26:20 2010 > >>>>>New Revision: 216016 > >>>>>URL: http://svn.freebsd.org/changeset/base/216016 > >>>>> > >>>>>Log: > >>>>> Define VM_KMEM_SIZE_MAX on sparc64. Otherwise kernel built with > >>>>> DEBUG_MEMGUARD panics early in kmeminit() with the message > >>>>> "kmem_suballoc: bad status return of 1" because of zero "size" > >>>>> argument > >>>>> passed to kmem_suballoc() due to "vm_kmem_size_max" being zero. > >>>>> > >>>>> The problem also exists on ia64. > >>>>> > >>>>>Modified: > >>>>> head/sys/sparc64/include/vmparam.h > >>>>> > >>>>>Modified: head/sys/sparc64/include/vmparam.h > >>>>> > >>>>> > >>>>============================================================================== > >>>> > >>>>>--- head/sys/sparc64/include/vmparam.h Sun Nov 28 18:59:52 2010 > >>>>> > >>>> (r216015) > >>>> > >>>>>+++ head/sys/sparc64/include/vmparam.h Sun Nov 28 19:26:20 2010 > >>>>> > >>>> (r216016) > >>>> > >>>>>@@ -237,6 +237,14 @@ > >>>>> #endif > >>>>> > >>>>> /* > >>>>>+ * Ceiling on amount of kmem_map kva space. > >>>>>+ */ > >>>>>+#ifndef VM_KMEM_SIZE_MAX > >>>>>+#define VM_KMEM_SIZE_MAX ((VM_MAX_KERNEL_ADDRESS - \ > >>>>>+ VM_MIN_KERNEL_ADDRESS + 1) * 3 / 5) > >>>>>+#endif > >>>>>+ > >>>>>+/* > >>>>> * Initial pagein size of beginning of executable file. > >>>>> */ > >>>>> #ifndef VM_INITIAL_PAGEIN > >>>>> > >>>>How was that value determined? > >>>> > >>>> > >>>I've just copied it from amd64 to be non-zero for now. Do you have a > >>>better > >>>idea of what it should look like? > >>> > >>> > >>Well, on sparc64 VM_MAX_KERNEL_ADDRESS already is dynamically adjusted > >>to the maximum appropriate for the specific CPU during the early cycles > >>of the kernel so I'd think one could just use VM_MAX_KERNEL_ADDRESS - > >>VM_MIN_KERNEL_ADDRESS for VM_KMEM_SIZE_MAX there, I'm not sure what > >>the intention of the ceiling provided by that macro actually is though > >>In any case, the commit message of r180210 which changed the amd64 > >>version to the current one talks about limiting the kmem map to 3.6GB > >>and while it also fails to explain where that value comes from it > >>looks rather amd64 specific and the formula used by the macro will > >>result in a different ceiling on sparc64 and thus inappropriate. I've > >>CC'ed alc@ who hopefully can shed some light on this. > >>Apart from this the actual bug here seems to be that memguard_fudge() > >>can't deal with a km_max being zero or that zero is passed to it as > >>kmeminit() allows for VM_KMEM_SIZE_MAX not being defined. > >> > >> > > > >Oops, forgot to actually CC alc@. > > > > There's nothing particularly amd64-specific about the definition. In > general, if you allow the kmem_map, which is basically the kernel's > heap, to consume the entire kernel address space as you propose, then > you're leaving no room for the buffer cache, thread stacks, pipes, and a > few other things. Since the cap on the kmem_map size as defined by > r180210 is a fraction of the overall kernel address space size, it > scales automatically with the kernel address space size and should be a > reasonable cap definition for most architectures. > > In the specific case of sparc64, I think it's fair to say that the > kernel virtual address is sufficiently large and the amount of physical > memory in any of the supported machines is small enough in comparison > that it hasn't mattered that a kmem_map cap doesn't exist, because most > of the aforementioned structures are scaled based on the amount of > physical memory. In fact, it probably won't matter any time soon. > > All of that said, I would suggest fixing memguard_fudge() and reverting > r216016 and the follow up change. All I think that is required to fix > memguard_fudge() is > > Index: vm/memguard.c > =================================================================== > --- vm/memguard.c (revision 216070) > +++ vm/memguard.c (working copy) > @@ -186,7 +186,7 @@ memguard_fudge(unsigned long km_size, unsigned lon > memguard_mapsize = round_page(memguard_mapsize); > if (memguard_mapsize / (2 * PAGE_SIZE) > mem_pgs) > memguard_mapsize = mem_pgs * 2 * PAGE_SIZE; > - if (km_size + memguard_mapsize > km_max) > + if (km_max > 0 && km_size + memguard_mapsize > km_max) > return (km_max); > return (km_size + memguard_mapsize); > } > Thanks but unfortunately this variant then still panics in kmem_suballoc() when called by memguard_init(): KDB: debugger backends: ddb KDB: current backend: ddb Copyright (c) 1992-2010 The FreeBSD Project. Copyright (c) 1979, 1980, 1983, 1986, 1988, 1989, 1991, 1992, 1993, 1994 The Regents of the University of California. All rights reserved. FreeBSD is a registered trademark of The FreeBSD Foundation. FreeBSD 9.0-CURRENT #17 r215249:216120M: Thu Dec 2 15:17:35 CET 2010 marius@v20z.zeist.de:/home/marius/co/build/head2/sparc64.sparc64/usr/home/m4 WARNING: WITNESS option enabled, expect reduced performance. panic: kmem_suballoc: bad status return of 1 cpuid = 0 KDB: enter: panic [ thread pid 0 tid 0 ] Stopped at 0xc03b04c0: ta %xcc, 1 db> bt Tracing pid 0 tid 0 td 0xc089ca10 (null)() at 0xc0371bac (null)() at 0xc054d2dc (null)() at 0xc0547dc8 (null)() at 0xc0359a78 (null)() at 0xc031e930 (null)() at 0xc0070028 Marius
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