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From: "H. Peter Anvin" <hpa@zytor.com>
To: Andi Kleen <ak@suse.de>
Cc: Ingo Molnar <mingo@elte.hu>,
	Alexander van Heukelum <heukelum@fastmail.fm>,
	Thomas Gleixner <tglx@linutronix.de>,
	LKML <linux-kernel@vger.kernel.org>,
	Alexander van Heukelum <heukelum@mailshack.com>
Subject: Re: [PATCH] reserve_early end-of-conventional-memory to 1MB II - some numbers to put it into perspective
Date: Wed, 27 Feb 2008 08:44:40 -0800	[thread overview]
Message-ID: <47C59378.6020608@zytor.com> (raw)
In-Reply-To: <47C575E4.7050206@suse.de>

Andi Kleen wrote:
> 
> Just to give some perspective of this:
> 
> On my laptop here
> 
>  BIOS-e820: 000000000009dc00 - 00000000000a0000 (reserved)
>  BIOS-e820: 00000000000d2000 - 0000000000100000 (reserved)
> 
> This means it reserves only ~193KB in the 640k-1MB area
> 
> With this patch it will reserve 384KB instead. This means 191KB
> are lost. While that doesn't sound too much it worth as much as
> 382 patches that reduce kernel code size by 512bytes or
> worth 3820 patches that reduce kernel code by 100 bytes in terms
> of memory consumption.
> 
> Now such kernel code size patches are always popular, but why undo that
> work by throwing away perfectly good memory elsewhere?
> 
> Or also the laptop kernel does
> 
> Freeing unused kernel memory: 340k freed
> 
> This means the 193KB now lost are worth 56% of the complete
> memory that is freed by __initdata/__init. Just maintaining
> these annotations is a lot of work, but why do all that if we
> then throw away than half as much memory as they save so easily?
> 

It doesn't waste any memory at all.

It arguably wastes some *address space*, but that's an entirely 
different thing.

Unless you have chipset-specific drivers to enable memory in the 
640-1024K memory area, there is nothing there.

	-hpa

  reply	other threads:[~2008-02-27 16:45 UTC|newest]

Thread overview: 62+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-24 17:46 [PATCH] Fix alignment of early reservation for EBDA Alexander van Heukelum
2008-02-24 19:27 ` Andi Kleen
2008-02-24 19:41 ` Ingo Molnar
2008-02-24 20:53   ` Alexander van Heukelum
2008-02-25  2:18 ` H. Peter Anvin
2008-02-25 16:54   ` Alexander van Heukelum
2008-02-25 17:01     ` Ingo Molnar
2008-02-25 18:07       ` [PATCH] reserve_early end-of-conventional-memory to 1MB Alexander van Heukelum
2008-02-25 18:13         ` H. Peter Anvin
2008-02-25 19:46           ` Alexander van Heukelum
2008-02-25 21:17             ` H. Peter Anvin
2008-02-26  9:30             ` Ingo Molnar
2008-02-27 14:26               ` Andi Kleen
2008-02-27 14:38               ` [PATCH] reserve_early end-of-conventional-memory to 1MB II - some numbers to put it into perspective Andi Kleen
2008-02-27 16:44                 ` H. Peter Anvin [this message]
2008-02-27 20:01                 ` Alexander van Heukelum
2008-02-28 13:13         ` [PATCH] reserve end-of-conventional-memory to 1MB on 32-bit Alexander van Heukelum
2008-02-28 13:28           ` [RFC] use realmode code to reserve end-of-conventional-memory to 1MB Alexander van Heukelum
2008-02-28 21:12             ` Ian Campbell
2008-02-28 21:14               ` H. Peter Anvin
2008-02-28 23:16                 ` Ian Campbell
2008-02-29 20:00                   ` Ingo Molnar
2008-03-04 11:41                   ` Mark McLoughlin
2008-03-04 14:33                     ` Ingo Molnar
2008-03-04 15:12                       ` Ian Campbell
2008-03-04 15:13                       ` Jeremy Fitzhardinge
2008-03-04 15:25                         ` Ingo Molnar
2008-03-04 16:02                           ` Jeremy Fitzhardinge
2008-03-04 16:15                             ` Ingo Molnar
2008-03-04 16:15                       ` Mark McLoughlin
2008-03-04 16:23                         ` Ingo Molnar
2008-03-04 17:44                   ` Jeremy Fitzhardinge
2008-03-05 15:59                   ` Eduardo Habkost
2008-03-05 16:08                     ` H. Peter Anvin
2008-03-05 16:53                       ` Eduardo Habkost
2008-03-05 17:28                         ` H. Peter Anvin
2008-03-05 17:28                           ` Jeremy Fitzhardinge
2008-03-05 17:38                             ` H. Peter Anvin
2008-03-05 16:38                     ` Jeremy Fitzhardinge
2008-03-05 17:27                       ` H. Peter Anvin
2008-02-28 21:09           ` [PATCH] reserve end-of-conventional-memory to 1MB on 32-bit Ian Campbell
2008-02-29 11:49             ` Alexander van Heukelum
2008-02-29 17:14               ` Mark McLoughlin
2008-02-29 18:38                 ` Alexander van Heukelum
2008-02-29 18:44                   ` H. Peter Anvin
2008-02-29 18:56                     ` Alexander van Heukelum
2008-02-29 22:06                   ` Mark McLoughlin
2008-02-29 22:26                     ` Alexander van Heukelum
2008-03-01 16:09                     ` [PATCH] reserve end-of-conventional-memory to 1MB on 32-bit v2 Alexander van Heukelum
2008-03-01 16:12                       ` [PATCH] reserve end-of-conventional-memory to 1MB on 64-bit add-on Alexander van Heukelum
2008-03-04 11:44                       ` [PATCH] reserve end-of-conventional-memory to 1MB on 32-bit v2 Mark McLoughlin
2008-03-04 13:31                         ` Alexander van Heukelum
2008-03-04 14:49                         ` Ingo Molnar
2008-03-04 15:16                           ` Mark McLoughlin
2008-03-04 15:24                             ` Ingo Molnar
2008-03-04 15:18                         ` Jeremy Fitzhardinge
2008-03-04 16:51                           ` Alexander van Heukelum
2008-03-04 17:05                             ` H. Peter Anvin
2008-03-04 17:11                             ` Jeremy Fitzhardinge
2008-03-04 18:57                               ` [PATCH] reserve end-of-conventional-memory to 1MB, 32-bit, use paravirt_enabled Alexander van Heukelum
2008-03-04 19:12                                 ` [PATCH] reserve end-of-conventional-memory to 1MB, 64-bit, " Alexander van Heukelum
2008-02-27 14:25     ` [PATCH] Fix alignment of early reservation for EBDA Andi Kleen

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