(2013/08/23 8:57), zhangwei(Jovi) wrote: > On 2013/8/23 0:42, Steven Rostedt wrote: >> On Fri, 09 Aug 2013 18:56:54 +0900 >> Masami Hiramatsu <masami.hiramatsu...@hitachi.com> wrote: >> >>> (2013/08/09 17:45), Namhyung Kim wrote: >>>> From: Namhyung Kim <namhyung....@lge.com> >>>> >>>> Fetching from user space should be done in a non-atomic context. So >>>> use a temporary buffer and copy its content to the ring buffer >>>> atomically. >>>> >>>> While at it, use __get_data_size() and store_trace_args() to reduce >>>> code duplication. >>> >>> I just concern using kmalloc() in the event handler. For fetching user >>> memory which can be swapped out, that is true. But most of the cases, >>> we can presume that it exists on the physical memory. >>> >> >> >> What about creating a per cpu buffer when uprobes are registered, and >> delete them when they are finished? Basically what trace_printk() does >> if it detects that there are users of trace_printk() in the kernel. >> Note, it does not deallocate them when finished, as it is never >> finished until reboot ;-) >> >> -- Steve >> > I also thought out this approach, but the issue is we cannot fetch user > memory into per-cpu buffer, because use per-cpu buffer should under > preempt disabled, and fetching user memory could sleep.
Hm, perhaps, we just need a "hot" buffer pool which can be allocate/free soon, and whan the pool shortage caller just wait or allocate new page from "cold" area, this is a.k.a. kmem_cache :) Anyway, kmem_cache/kmalloc looks so heavy to just allocate temporally buffers for trace handler (and also, those have tracepoints), so I think you may just need a memory pool whose has enough number of slots with a semaphore (which will wait if the all slots are currently used). Thank you, -- Masami HIRAMATSU IT Management Research Dept. Linux Technology Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: masami.hiramatsu...@hitachi.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
