linux-kernel - Re: [PATCH 0/5] kstrdup optimization

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Message-Id: <20150113153731.43eefac721964d165396e5af@linux-foundation.org>
Date:	Tue, 13 Jan 2015 15:37:31 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Andrzej Hajda <a.hajda@...sung.com>
Cc:	linux-mm@...ck.org, Marek Szyprowski <m.szyprowski@...sung.com>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	linux-kernel@...r.kernel.org, andi@...stfloor.org, andi@...as.de,
	Mike Turquette <mturquette@...aro.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH 0/5] kstrdup optimization

On Mon, 12 Jan 2015 10:18:38 +0100 Andrzej Hajda <a.hajda@...sung.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?


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