Re: [PATCH 0/5] kstrdup optimization

Andrew Morton
2015-01-13T23:37:34Z

On Mon, 12 Jan 2015 10:18:38 +0100 Andrzej Hajda <a.hajda@samsung.com> wrote:

> Hi,
>
> 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.
> 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.

That's a lot of memory. I wonder where it's all going to. sysfs,
probably?

What the heck does (the cheerily undocumented) KERNFS_STATIC_NAME do
and can we remove it if this patchset is in place?