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SubjectRe: [PATCH 05/10] mm, util: Use dup_user to duplicate user memory
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Hi Andrew,

On Tue, Sep 25, 2012 at 6:29 PM, Andrew Morton
<akpm@linux-foundation.org> wrote:
> On Sat, 8 Sep 2012 17:47:54 -0300
> Ezequiel Garcia <elezegarcia@gmail.com> wrote:
>
>> Previously the strndup_user allocation was being done through memdup_user,
>> and the caller was wrongly traced as being strndup_user
>> (the correct trace must report the caller of strndup_user).
>>
>> This is a common problem: in order to get accurate callsite tracing,
>> a utils function can't allocate through another utils function,
>> but instead do the allocation himself (or inlined).
>>
>> Here we fix this by creating an always inlined dup_user() function to
>> performed the real allocation and to be used by memdup_user and strndup_user.
>
> This patch increases util.o's text size by 238 bytes. A larger kernel
> with a worsened cache footprint.
>
> And we did this to get marginally improved tracing output? This sounds
> like a bad tradeoff to me.
>

Mmm, that's bad tradeoff indeed.
It's certainly odd since the patch shouldn't increase the text size
*that* much.
Is it too much to ask that you send your kernel config and gcc version.

My compilation (x86 kernel in gcc 4.7.1) shows a kernel less bloated:

$ readelf -s util-dup-user.o | grep dup_user
161: 00001c10 108 FUNC GLOBAL DEFAULT 1 memdup_user
169: 00001df0 159 FUNC GLOBAL DEFAULT 1 strndup_user
$ readelf -s util.o | grep dup_user
161: 00001c10 108 FUNC GLOBAL DEFAULT 1 memdup_user
169: 00001df0 98 FUNC GLOBAL DEFAULT 1 strndup_user

$ size util.o
text data bss dec hex filename
18319 2077 0 20396 4fac util.o
$ size util-dup-user.o
text data bss dec hex filename
18367 2077 0 20444 4fdc util-dup-user.o

Am I doing anything wrong?
If you still feel this is unnecessary bloatness, perhaps I could think of
something depending on CONFIG_TRACING (though I know
we all hate those nasty ifdefs).

Anyway, thanks for the review,
Ezequiel.


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