linux-kernel - Re: [PATCH 2/2] tracing: Resize tgid_map to PID_MAX_LIMIT, not PID_MAX

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Message-ID: <CAJWu+ooJzcTFBFPSqWE5oHe2_4Gt_GHXftcXutk5mm-UX_hUUA@mail.gmail.com>
Date:   Wed, 30 Jun 2021 18:34:11 -0400
From:   Joel Fernandes <joelaf@...gle.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Paul Burton <paulburton@...gle.com>, linux-kernel@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>, stable@...r.kernel.org
Subject: Re: [PATCH 2/2] tracing: Resize tgid_map to PID_MAX_LIMIT, not PID_MAX_DEFAULT

On Wed, Jun 30, 2021 at 5:34 PM Steven Rostedt <rostedt@...dmis.org> wrote:
[..]
> > Having said that I think taking a similar approach to saved_cmdlines
> > would be better than what we have now, though I'm not sure whether it'll
> > be sufficient to actually be usable for me. My use case is grouping
> > threads into processes when displaying scheduling information, and
> > experience tells me that if any threads don't get grouped appropriately
> > the result will be questions.
>
> I found a few bugs recently in the saved_cmdlines that were causing a
> much higher miss rate, but now it's been rather accurate. I wonder how
> much pain that's been causing you?
>
> Anyway, I'll wait to hear what Joel says on this. If he thinks this is
> worth 16M of memory when enabled, I may take it.

I am not a huge fan of the 16M, in Android we enable this feature on
all devices. Low end Android devices traced in the field are sometimes
1 GB and the added memory pressure may be unwelcome. Very least, maybe
make it optional only for folks who increase pid_max?

thanks,
-Joel