linux-kernel - Re: [RFC PATCH v3 00/18] dynamic debug diet plan

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Message-ID: <CAJfuBxyJHu3JdZ++0RU3DEDUS-i-4iT990P+zihFG_nKfyjVFA@mail.gmail.com>
Date:   Sat, 1 May 2021 20:16:59 -0600
From:   jim.cromie@...il.com
To:     Andi Kleen <ak@...ux.intel.com>
Cc:     Jason Baron <jbaron@...mai.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v3 00/18] dynamic debug diet plan

On Thu, Mar 18, 2021 at 10:12 PM Andi Kleen <ak@...ux.intel.com> wrote:
>
> Jim Cromie <jim.cromie@...il.com> writes:
>
> > CONFIG_DYNAMIC_DEBUG creates a struct _ddebug (56 bytes) for each
> > callsite, which includes 3 pointers to: module, filename, function.
> > These are repetetive, and compressible, this patch series goes about
> > doing that, it:
>
> So how much memory does it actually save?
> -Andi

sorry for late reply, html mode got switched on and I didnt see kickback

on my laptop/build, master has 165kb, about 70k is the compressible data,
RLE column-wize could get close to 60% on my data. so ~40kb ?

3 things to do to get the savings:
figure the compression,
figure the hash holding enabled/used/expanded pr_debug decorations
(maybe optional, depending on indexed/seek decompress time)
drop the site pointer, with some anonymous union struct combo to blend
header with callsites cleanly