Date: Tue, 18 Dec 2012 03:59:31 -0600 From: Alan Cox <alc@rice.edu> To: Oleksandr Tymoshenko <gonzo@bluezbox.com> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org, Andre Oppermann <andre@freebsd.org> Subject: Re: svn commit: r243631 - in head/sys: kern sys Message-ID: <50D03E83.8060908@rice.edu> In-Reply-To: <330405A1-312A-45A5-BB86-4969478D8BBD@bluezbox.com> References: <201211272119.qARLJxXV061083@svn.freebsd.org> <ABB3E29B-91F3-4C25-8FAB-869BBD7459E1@bluezbox.com> <50C1BC90.90106@freebsd.org> <50C25A27.4060007@bluezbox.com> <50C26331.6030504@freebsd.org> <50C26AE9.4020600@bluezbox.com> <50C3A3D3.9000804@freebsd.org> <50C3AF72.4010902@rice.edu> <330405A1-312A-45A5-BB86-4969478D8BBD@bluezbox.com>
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On 12/17/2012 23:40, Oleksandr Tymoshenko wrote: > On 2012-12-08, at 1:21 PM, Alan Cox <alc@rice.edu> wrote: > >> On 12/08/2012 14:32, Andre Oppermann wrote: > .. skipped .. > >>> The trouble seems to come from NSFBUFS which is (512 + maxusers * 16) >>> resulting in a kernel map of (512 + 400 * 16) * PAGE_SIZE = 27MB. This >>> seem to be pushing it with the smaller ARM kmap layout. >>> >>> Does it boot and run when you set the tunable kern.ipc.nsfbufs=3500? >>> >>> ARM does have a direct map mode as well which doesn't require the >>> allocation >>> of sfbufs. I'm not sure which other problems that approach has. >>> >> >> Only a few (3?) platforms use it. It reduces the size of the user >> address space, and translation between physical addresses and direct map >> addresses is not computationally trivial as it is on other >> architectures, e.g., amd64, ia64. However, it does try to use large >> page mappings. >> >> >>> Hopefully alc@ (added to cc) can answer that and also why the kmap of >>> 27MB >>> manages to wrench the ARM kernel. >>> >> >> Arm does not define caps on either the buffer map size (param.h) or the >> kmem map size (vmparam.h). It would probably make sense to copy these >> definitions from i386. > > Adding caps didn't help. I did some digging and found out that although address range > 0xc0000000 .. 0xffffffff is indeed valid for ARM in general actual KVA space varies for > each specific hardware platform. This "real" KVA is defined by <virtual_avail, virtual_end> > pair and ifI use them instead of <VM_MIN_KERNEL_ADDRESS, VM_MAX_KERNEL_ADDRESS> > in init_param2 function my pandaboard successfully boots. Since former pair is used for defining > kernel_map boundaries I believe it should be used for auto tuning as well. That makes sense. However, "virtual_avail" isn't the start of the kernel address space. The kernel map always starts at VM_MIN_KERNEL_ADDRESS. (See kmem_init().) "virtual_avail" represents the next unallocated virtual address in the kernel address space at an early point in initialization. "virtual_avail" and "virtual_end" aren't used after that, or outside the VM system. Please use vm_map_min(kernel_map) and vm_map_max(kernel_map) instead. That said, I would still add caps on the buffer map and kmem map size. As memory sizes on arm systems grow, you'll eventually need them, just like we did on i386. Alanhome | help
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