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Date: Mon, 2 Mar 2015 13:43:29 -0500
From: Steven Rostedt <rostedt@goodmis.org>
To: Alexei Starovoitov <ast@plumgrid.com>
Cc: Tom Zanussi <tom.zanussi@linux.intel.com>,
        Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
        Namhyung Kim <namhyung@kernel.org>, Andi Kleen <andi@firstfloor.org>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 07/15] mm: Add ___GFP_NOTRACE
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On Mon, 2 Mar 2015 10:12:32 -0800
Alexei Starovoitov <ast@plumgrid.com> wrote:

> I'm not sure what would be the meaning of hash map that has all
> elements pre-allocated...
> As I'm reading your cover letter, I agree, we need to find a way
> to call kmalloc_notrace-like from tracepoints.
> Not sure that patch 8 style of duplicating the functions is clean.
> Can we keep kmalloc/kfree as-is and do something like
> if (in_tracepoint()) check inside ftrace_raw_kmalloc*  ?

I'm strongly against this. You should not be doing anything in a
tracepoint that you can't do from NMI context. And calling kmalloc
happens to be one of them.

Not to mention, kmalloc is a hot path, and tracing must not have any
impact on it (no extra if statements).

-- Steve

> so that kmalloc will be traced but calls to kmalloc from inside
> tracepoints will be automatically suppressed ?