lkml.org 
[lkml]   [2015]   [Jan]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH 0/5] kstrdup optimization
From
On Mon, Jan 12, 2015 at 10:18 AM, Andrzej Hajda <a.hajda@samsung.com> wrote:
> kstrdup if often used to duplicate strings where neither source neither
> destination will be ever modified. In such case we can just reuse the source
> instead of duplicating it. The problem is that we must be sure that
> the source is non-modifiable and its life-time is long enough.
>
> I suspect the good candidates for such strings are strings located in kernel
> .rodata section, they cannot be modifed because the section is read-only and
> their life-time is equal to kernel life-time.
>
> This small patchset proposes alternative version of kstrdup - kstrdup_const,
> which returns source string if it is located in .rodata otherwise it fallbacks
> to kstrdup.

It also introduces kfree_const(const void *x).

As kfree_const() has the exact same signature as kfree(), the risk of
accidentally passing pointers returned from kstrdup_const() to kfree() seems
high, which may lead to memory corruption if the pointer doesn't point to
allocated memory.

> To verify if the source is in .rodata function checks if the address is between
> sentinels __start_rodata, __end_rodata. I guess it should work with all
> architectures.
>
> The main patch is accompanied by four patches constifying kstrdup for cases
> where situtation described above happens frequently.
>
> As I have tested the patchset on mobile platform (exynos4210-trats) it saves
> 3272 string allocations. Since minimal allocation is 32 or 64 bytes depending
> on Kconfig options the patchset saves respectively about 100KB or 200KB of memory.

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds


\
 
 \ /
  Last update: 2015-01-12 22:01    [W:0.130 / U:0.864 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site