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Date: Sat, 10 Aug 2013 09:41:44 +0800 From: "zhangwei(Jovi)" <jovi.zhangwei@...il.com> To: Oleg Nesterov <oleg@...hat.com> Cc: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>, Steven Rostedt <rostedt@...dmis.org>, Namhyung Kim <namhyung@...nel.org>, Namhyung Kim <namhyung.kim@....com>, Hyeoncheol Lee <cheol.lee@....com>, LKML <linux-kernel@...r.kernel.org>, Srikar Dronamraju <srikar@...ux.vnet.ibm.com>, "zhangwei(Jovi)" <jovi.zhangwei@...wei.com>, Arnaldo Carvalho de Melo <acme@...stprotocols.net> Subject: Re: [PATCH 10/13] tracing/uprobes: Fetch args before reserving a ring buffer On Sat, Aug 10, 2013 at 9:26 AM, zhangwei(Jovi) <jovi.zhangwei@...il.com> wrote: > On Sat, Aug 10, 2013 at 12:20 AM, Oleg Nesterov <oleg@...hat.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. :) > > Thanks. >> >> >> Steven, Jovi, what should we do with that patch? It seems that it >> was forgotten. >> >> I can take these patches into my ubprobes branch and then ask Ingo >> to pull. But this will complicate the routing of the new changes >> like this. >> >> Oleg. -- 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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