[PATCH 0/5] kstrdup optimization

Andrzej Hajda
2015-01-12T09:19:58Z

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.

The patchset is based on 3.19-rc4.

This patchset have been already sent to the list as RFC.
Current version have following changes:
- added missing export,
- added kerneldocs,
- constified kstrdup in VFS devname allocation.

Regards
Andrzej

Andrzej Hajda (5):
mm/util: add kstrdup_const
kernfs: convert node name allocation to kstrdup_const
clk: convert clock name allocations to kstrdup_const
mm/slab: convert cache name allocations to kstrdup_const
fs/namespace: convert devname allocation to kstrdup_const

drivers/clk/clk.c | 12 ++++++------
fs/kernfs/dir.c | 12 ++++++------
fs/namespace.c | 6 +++---
include/linux/string.h | 3 +++
mm/slab_common.c | 6 +++---
mm/util.c | 38 ++++++++++++++++++++++++++++++++++++++
6 files changed, 59 insertions(+), 18 deletions(-)

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1.9.1