linux-kernel - Re: [PATCH 4/4] export: avoid code duplication in include/linux/export.h

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Message-ID: <20191011154311.GA192647@google.com>
Date:   Fri, 11 Oct 2019 16:43:11 +0100
From:   Matthias Maennich <maennich@...gle.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, kernel-team@...roid.com,
        Jessica Yu <jeyu@...nel.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Martijn Coenen <maco@...roid.com>,
        Lucas De Marchi <lucas.de.marchi@...il.com>,
        Shaun Ruffell <sruffell@...ffell.net>,
        Will Deacon <will@...nel.org>, linux-kbuild@...r.kernel.org,
        linux-modules@...r.kernel.org,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: Re: [PATCH 4/4] export: avoid code duplication in
 include/linux/export.h

On Fri, Oct 11, 2019 at 05:31:27PM +0200, Greg Kroah-Hartman wrote:
>On Thu, Oct 10, 2019 at 04:14:43PM +0100, Matthias Maennich wrote:
>> Now that the namespace value is not part of the __ksymtab entry name
>> anymore, we can simplify the implementation of EXPORT_SYMBOL*. By
>> allowing the empty string "" to represent 'no namespace', we can unify
>> the implementation and drop a lot redundant code.  That increases
>> readability and maintainability.
>>
>> As Masahiro pointed out earlier,
>> "The drawback of this change is, it grows the code size. When the symbol
>> has no namespace, sym->namespace was previously NULL, but it is now am
>> empty string "". So, it increases 1 byte for every no namespace
>> EXPORT_SYMBOL. A typical kernel configuration has 10K exported symbols,
>> so it increases 10KB in rough estimation."
>
>10Kb of non-swapable memory isn't good.  But if you care about that, you
>can get it back with the option to compile away any non-used symbols,
>and that shouldn't be affected by this change, right?

Rasmus suggested to put the 'aMS' flags on the __ksymtab_strings section
to mitigate this:
https://lore.kernel.org/lkml/f2e28d6b-77c5-5fe2-0bc4-b24955de9954@rasmusvillemoes.dk/

I was not yet able to properly test this, so I did not include it in
this series. As I said in the cover letter, this 4th patch might be
optional for 5.4. So, we could defer it to a later time when we have
addressed that properly.

Cheers,
Matthias

>
>That being said, the code is a lot cleaner, so I have no objection to
>it.
>
>Reviewed-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>