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Date: Wed, 22 Jul 2009 22:26:05 -0400 (EDT) From: Steven Rostedt <rostedt@...dmis.org> To: Andrew Morton <akpm@...ux-foundation.org> cc: Roland Dreier <rdreier@...co.com>, linux-kernel@...r.kernel.org, jsquyres@...co.com Subject: Re: [PATCH/RFC] ummunot: Userspace support for MMU notifications On Wed, 22 Jul 2009, Andrew Morton wrote: > On Wed, 22 Jul 2009 12:27:42 -0700 > Roland Dreier <rdreier@...co.com> wrote: > > > > > 1. ioctl() to register/unregister an address range to watch in the > > > > kernel (cf struct ummunot_register_ioctl in <linux/ummunot.h>). > > > > > > > > 2. read() to retrieve events generated when a mapping in a watched > > > > address range is invalidated (cf struct ummunot_event in > > > > <linux/ummunot.h>). select()/poll()/epoll() and SIGIO are handled > > > > for this IO. > > > > > > > > 3. mmap() one page at offset 0 to map a kernel page that contains a > > > > generation counter that is incremented each time an event is > > > > generated. This allows userspace to have a fast path that checks > > > > that no events have occurred without a system call. Looks like a vsyscall to me. > > > > > > If you stand back and squint, each of 1, 2 and 3 are things which the > > > kernel already provides for the delivery of ftrace events to userspace. > > > > > > Did you look at reusing all that stuff? > > > > No, not really... will investigate a bit further. Any pointers to how > > the ftrace stuff might work? > > I know who to cc ;) You would wouldn't you ;-) > > > Specifically how #3 maps to ftrace is a > > little obscure to me; and also as I understand it, ftrace is controlled > > through debugfs, which means there's a bit of hassle to make this usable > > on a default install. And also I'm not sure how the ftrace control path On Fedora 11 (early ftrace kernel) # mount -t debugfs nodev /sys/kernel/debug # ls /sys/kernel/debug/tracing available_filter_functions set_ftrace_filter available_tracers set_ftrace_notrace buffer_size_kb set_ftrace_pid current_tracer stack_max_size dyn_ftrace_total_info stack_trace failures sysprof_sample_period latency_trace trace process_follow_pid trace_marker process_trace_lifecycle trace_options process_trace_README trace_pipe process_trace_signals tracing_cpumask process_trace_syscalls tracing_enabled process_trace_taskcomm_filter tracing_max_latency process_trace_uid_filter tracing_on README tracing_thresh Not too hard > > really maps to "here's a 100 address ranges I'd like events for". Now to boot into a more recent kernel: # cd /sys/kernel/debug/tracing # echo "ptr > 0xffffffff81100000 && ptr < 0xffffffff8113000" > events/kmem/kmalloc/filter # echo 1 > events/kmem/kmalloc/enable # cat events/kmem/kmalloc/filter ptr > 0xffffffff81100000 && ptr < 0xffffffff81130000 # cat trace # tracer: nop # # TASK-PID CPU# TIMESTAMP FUNCTION # | | | | | bash-6652 [002] 80345.390536: kmalloc: call_site=ffffffff810d76e1 ptr=ffff88001e8e7c80 bytes_req=53 bytes_alloc=64 gfp_flags=GFP_KERNEL bash-6652 [002] 80345.390542: kmalloc: call_site=ffffffff810ba480 ptr=ffff88003c5a2700 bytes_req=32 bytes_alloc=32 gfp_flags=GFP_KERNEL bash-6652 [002] 80345.390543: kmalloc: call_site=ffffffff810d76e1 ptr=ffff88003c5a2540 bytes_req=4 bytes_alloc=32 gfp_flags=GFP_KERNEL bash-6652 [002] 80345.390544: kmalloc: call_site=ffffffff810ba210 ptr=ffff8800318c4d00 bytes_req=24 bytes_alloc=32 gfp_flags=GFP_KERNEL bash-6652 [002] 80345.390550: kmalloc: call_site=ffffffff810ba480 ptr=ffff8800318c43c0 bytes_req=32 bytes_alloc=32 gfp_flags=GFP_KERNEL bash-6652 [002] 80345.390551: kmalloc: call_site=ffffffff810d76e1 ptr=ffff8800318c4ca0 bytes_req=19 bytes_alloc=32 gfp_flags=GFP_KERNEL bash-6652 [002] 80345.390552: kmalloc: call_site=ffffffff810ba320 ptr=ffff8800318c4d00 bytes_req=32 bytes_alloc=32 gfp_flags=GFP_KERNEL bash-6652 [002] 80345.390552: kmalloc: call_site=ffffffff810ba210 ptr=ffff8800318c4e20 bytes_req=24 bytes_alloc=32 gfp_flags=GFP_KERNEL bash-6652 [002] 80345.390554: kmalloc: call_site=ffffffff810ba480 ptr=ffff8800318c4400 bytes_req=32 bytes_alloc=32 gfp_flags=GFP_KERNEL bash-6652 [002] 80345.390555: kmalloc: call_site=ffffffff810d76e1 ptr=ffff8800318c4380 bytes_req=4 bytes_alloc=32 gfp_flags=GFP_KERNEL bash-6652 [002] 80345.390555: kmalloc: call_site=ffffffff810ba210 ptr=ffff8800318c42e0 bytes_req=24 bytes_alloc=32 gfp_flags=GFP_KERNEL bash-6652 [002] 80345.390561: kmalloc: call_site=ffffffff810ba480 ptr=ffff8800318c4d20 bytes_req=32 bytes_alloc=32 gfp_flags=GFP_KERNEL bash-6652 [002] 80345.390562: kmalloc: call_site=ffffffff810d76e1 ptr=ffff8800318c4240 bytes_req=19 bytes_alloc=32 gfp_flags=GFP_KERNEL bash-6652 [002] 80345.390563: kmalloc: call_site=ffffffff810ba320 ptr=ffff8800318c42e0 bytes_req=32 bytes_alloc=32 gfp_flags=GFP_KERNEL bash-6652 [002] 80345.390563: kmalloc: call_site=ffffffff810ba320 ptr=ffff8800318c4e20 bytes_req=32 bytes_alloc=32 gfp_flags=GFP_KERNEL bash-6652 [002] 80345.390566: kmalloc: call_site=ffffffff810bb0ee ptr=ffff88003d4e2680 bytes_req=176 bytes_alloc=192 gfp_flags=GFP_KERNEL|GFP_ZERO bash-6652 [002] 80345.390566: kmalloc: call_site=ffffffff810d76e1 ptr=ffff8800318c42c0 bytes_req=4 bytes_alloc=32 gfp_flags=GFP_KERNEL bash-6652 [002] 80345.390570: kmalloc: call_site=ffffffff810d76e1 ptr=ffff8800285405c0 bytes_req=4 bytes_alloc=32 gfp_flags=GFP_KERNEL bash-6652 [002] 80345.390574: kmalloc: call_site=ffffffff810bb320 ptr=ffff88003d4e2680 bytes_req=176 bytes_alloc=192 gfp_flags=GFP_KERNEL|GFP_ZERO > > > > So at a first glance after unsquinting a bit I'm not sure how good the > > fit really is. Well, if you need to add hooks, definitely at least use tracepoints. (see the TRACE_EVENT code in include/trace/events/*.h) I'm not exactly sure what requirements you have, but it may be something we can work together on. Eliminate some duplicate code, or at least, ftrace can piggy back on it ;-) > > Oh. Here was I hoping that all that code was about to become useful. > <runs away> You better run! -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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