Messages in this thread | | | Date | Sat, 10 Aug 2013 22:06:16 +0800 | Subject | Re: [PATCH 10/13] tracing/uprobes: Fetch args before reserving a ring buffer | From | "zhangwei(Jovi)" <> |
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On Sat, Aug 10, 2013 at 9:41 AM, zhangwei(Jovi) <jovi.zhangwei@gmail.com> wrote: > On Sat, Aug 10, 2013 at 9:26 AM, zhangwei(Jovi) <jovi.zhangwei@gmail.com> wrote: >> On Sat, Aug 10, 2013 at 12:20 AM, Oleg Nesterov <oleg@redhat.com> wrote: >>> >>> Sorry, I didn't read this series yet. Not that I think this needs my >>> help, but I'll try to do this a later... >>> >>> On 08/09, Masami Hiramatsu wrote: >>> > >>> > I just concern using kmalloc() in the event handler. >>> >>> GFP_KERNEL should be fine for uprobe handler. >>> >>> However, iirc this conflicts with the patches from Jovi, >>> "Support ftrace_event_file base multibuffer" adds rcu_read_lock() >>> around uprobe_trace_print(). >> >> (Sorry about html text rejected by kernel.org, send again with plain text.) >> >> Then we might need to call kmalloc before rcu_read_lock, also call kfree >> after rcu_read_unlock. >> >> And it's not needed to call kmalloc for each instances in multi-buffer >> case, just >> kmalloc once is enough. >> >> I also have same concern about use kmalloc in uprobe handler, use kmalloc >> in uprobe handler seems have a little overhead, why not pre-allocate one page >> static memory for temp buffer(perhaps trace_uprobe based)? one page size >> would be enough for all uprobe args storage, then we don't need to call >> kmalloc in that "fast path". >> > forgotten to say, that pre-allocated buffer would need to be per-cpu, to prevent > buffer corruption. > > It's a memory space vs. performance trade-off problem. :) > Oops, I missed the per-cpu buffer operation still need preempt_disable, ignore this part of my comments, now I agree kmalloc in uprobe handler is needed.
jovi.
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