Messages in this thread | | | Date | Fri, 7 Nov 2008 09:53:52 +0100 | From | Ingo Molnar <> | Subject | Re: [patch] add /proc/pid/stack to dump task's stack trace |
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* Alexey Dobriyan <adobriyan@gmail.com> wrote:
> On Fri, Nov 07, 2008 at 09:32:49AM +0100, Ingo Molnar wrote: > > > > * Alexey Dobriyan <adobriyan@gmail.com> wrote: > > > > > On Fri, Nov 07, 2008 at 08:59:25AM +0100, Ingo Molnar wrote: > > > > > > > > * Ingo Molnar <mingo@elte.hu> wrote: > > > > > > > > > > > + * buffer size used for proc read. See proc_info_read(). > > > > > > > + * 4K page size but our output routines use some slack for overruns > > > > > > > + */ > > > > > > > +#define PROC_BLOCK_SIZE (3*1024) > > > > > > > > > > That sounds like a proper limit - the hard limit for this particular > > > > > printout function is 4096-170, so we are well within the > > > > > PROC_BLOCK_SIZE range. > > > > > > > > ok, i've added Ken's patch to tip/core/stacktrace and started testing > > > > it. > > > > > > > > Alexey, i've added your Acked-by because you appeared to like the > > > > patch - let me know if i should remove it. > > > > > > Of course, I don't like it! > > > > > > Switch to seqfiles, add entry in TID table as well. > > > > > > The idea is good, though. > > > > oh well - Ken, could you please switch it to seqfiles? > > > > It should be something like this to convert the currently sweet and > > trivial function into a much more complex seqfile iterator splitup: > > > > - the ::start method does the kmalloc of a loop state structure like > > this: > > > > { > > struct stack_trace backtrace; > > unsigned long entries[MAX_STACK_TRACE_DEPTH]; > > > > int iterator; > > } > > > > and saves the trace. (struct stack_trace trace can be on-stack, it's > > only needed for the save_stack_trace() - and we keep the entries > > after that.) > > > > - the ::stop method does the kfree of the loop state. > > > > - the ::show method prints a single line, based on ->entries[->iterator] > > > > - the ::next method does ->iterator++, and returns NULL if iterator > > reaches ->backtrace.nr_entries. > > > > it will be more source code, larger kernel image, it will be more > > fragile and will be harder to review, and it wont actually matter in > > practice because 99.9999% of the backtraces we care about have a size > > smaller than 3K. (and where they get larger clipping them to the first > > 3K is perfectly fine) > > Or you can do all of this in ->show(), without start/next/stop: > > for (i = 0; i < N; i++) > seq_printf(m, "[<%p>] %pS\n", x, x);
hm, is that preferred over the current fs/proc/base.c code?
If that's the preferred way of doing these things, why arent all the single-page procfs functions converted over to seq_file:
#ifdef CONFIG_KALLSYMS INF("wchan", S_IRUGO, pid_wchan), #endif +#ifdef CONFIG_STACKTRACE + INF("stack", S_IRUSR, pid_stack), +#endif #ifdef CONFIG_SCHEDSTATS INF("schedstat", S_IRUGO, pid_schedstat), #endif
?
Really, please realize what happened here. All this unnecessary work comes from Ken just having done the _natural_ thing when extending the existing upstream code: using the existing fs/proc/base.c methods as a template to write new code. If those templates use outdated APIs, then new code will be "outdated" too - and this confusion will go on forever.
Ingo
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