linux-kernel - Re: [PATCH RESEND] trace_uprobe: support reference counter in fd-based uprobe

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Message-ID: <C9D064BF-BFB0-409E-B470-1128B570A92D@fb.com>
Date:   Fri, 28 Sep 2018 14:50:23 +0000
From:   Song Liu <songliubraving@...com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     lkml <linux-kernel@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        "Naveen N . Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH RESEND] trace_uprobe: support reference counter in
 fd-based uprobe



> On Sep 28, 2018, at 12:52 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> 
> On Fri, Sep 28, 2018 at 07:23:20AM +0000, Song Liu wrote:
>> Hi Peter,
>>> #ifdef CONFIG_UPROBE_EVENTS
>>> +PMU_FORMAT_ATTR(ref_ctr_offset, "config:63-24");
>> 
>> I guess you meant this part? This is for uprobe only, so I put
>> it here. 
> 
> Ah,.. right you are.
> 
> You seem to have the bitfield backwards, does that mean we should write
> the bits in backwards too? Seems a tad loopy if you ask me.
> 
> Did you instead mean: "config:24-63" ? Also, why 40 bits? 32 seems like
> a much more natural amount.

I guess it should be "config:24-63". I didn't realize the bit order here. 
I picked 40 bits files up to 1 TB. 32 bits should be also be enough for 
most cases. Let me fix these in v2. 

Thanks,
Song