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Subject: Re: [RFC 0/2] Delay initializing of large sections of memory
From: "H. Peter Anvin" <hpa@zytor.com>
Date: Fri, 21 Jun 2013 13:08:06 -0700
To: Nathan Zimmer <nzimmer@sgi.com>
CC: Greg KH <gregkh@linuxfoundation.org>, holt@sgi.com, travis@sgi.com,
        rob@landley.net, tglx@linutronix.de, mingo@redhat.com,
        yinghai@kernel.org, akpm@linux-foundation.org, x86@kernel.org,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org
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Is this init code?  32K of unconditional runtime addition isn't completely trivial.

Nathan Zimmer <nzimmer@sgi.com> wrote:

>On 06/21/2013 12:28 PM, H. Peter Anvin wrote:
>> On 06/21/2013 10:18 AM, Nathan Zimmer wrote:
>>>> Since you made it a compile time option, it would be good to know
>how
>>>> much code it adds, but otherwise I agree with Greg here... this
>really
>>>> shouldn't need to be an option.  It *especially* shouldn't need to
>be a
>>>> hand-set runtime option (which looks quite complex, to boot.)
>>> The patchset as a whole is just over 400 lines so it doesn't add
>alot.
>>> If I were to pull the .config option it would probably remove 30
>lines.
>> I'm more concerned about bytes of code.
>Oh, The difference is just under 32k.
>371843425 Jun 21 14:08 vmlinux.o /* DELAY_MEM_INIT is not set  */
>371875600 Jun 21 14:36 vmlinux.o /* DELAY_MEM_INIT=y */
>
>>
>>> The command line option is too complex but some of the data I
>haven't
>>> found a way to get at runtime yet.
>> I think that is probably key.
>>
>>>> I suspect the cutoff for this should be a lot lower than 8 TB even,
>more
>>>> like 128 GB or so.  The only concern is to not set the cutoff so
>low
>>>> that we can end up running out of memory or with suboptimal NUMA
>>>> placement just because of this.
>>> Even at lower amounts of ram there is an positive impact.I it knocks
>>> time off
>>> boot even at as small as a 1TB of ram.
>> I am not surprised.
>>
>> 	-hpa
>>

-- 
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