Messages in this thread | | | Date | Tue, 25 Sep 2012 22:15:38 -0300 | Subject | Re: [PATCH 05/10] mm, util: Use dup_user to duplicate user memory | From | Ezequiel Garcia <> |
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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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