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From: ebiederm@xmission.com (Eric W. Biederman)
To: "Satyam Sharma" <satyam.sharma@gmail.com>
Cc: "Pekka Enberg" <penberg@cs.helsinki.fi>,
       "Michael Tokarev" <mjt@tls.msk.ru>,
       "Shani Moideen" <shani.moideen@wipro.com>, ebiederm@xmission.com,
       linux-kernel@vger.kernel.org, kernel-janitors@lists.osdl.org
Subject: Re: [KJ PATCH] Replacing memset(<addr>,0,PAGE_SIZE) with clear_page() in kernel/kexec.c
References: <1178621444.3598.15.camel@shani-win>
	<46405AB6.6040901@msgid.tls.msk.ru>
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	<a781481a0705081013q7b54906dsdf28d922e198a463@mail.gmail.com>
Date: Tue, 08 May 2007 11:40:53 -0600
In-Reply-To: <a781481a0705081013q7b54906dsdf28d922e198a463@mail.gmail.com>
	(Satyam Sharma's message of "Tue, 8 May 2007 10:13:52 -0700")
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"Satyam Sharma" <satyam.sharma@gmail.com> writes:

> On 5/8/07, Pekka Enberg <penberg@cs.helsinki.fi> wrote:
>> Shani Moideen wrote:
>> > >                 ptr = kmap(page);
>> > > -               memset(ptr, 0, PAGE_SIZE);
>> > > +               clear_page(ptr);
>>
>> On 5/8/07, Michael Tokarev <mjt@tls.msk.ru> wrote:
>> > I wonder if it's worth to invent kzmap() or something like that... ;)
>>
>> I am counting 59 kmap + memset pairs in the kernel, so perhaps it is
>> worth it to reduce kernel text size.
>
> Stuff of the sort already exists. Look for clear_highpage(),
> clear_user_highpage() and memclear_highpage_flush (recently renamed to
> zero_user_page, see -mm). But they all use kmap_atomic() -- kmap()
> variants would have to be added. Also, they're all inlines, so I'm not
> sure you'd be able to cut down text size, but still getting rid of
> open-coding is always good.

In this instance a clear_page variant should be ok.  The combined
variants are likely not because I use the mapping after it is cleared.

Eric



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