From: "H. Peter Anvin" <hpa@zytor.com>
To: Tejun Heo <tj@kernel.org>
Cc: Yinghai Lu <yinghai@kernel.org>,
x86@kernel.org, Ingo Molnar <mingo@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
linux-kernel@vger.kernel.org
Subject: Re: questions about init_memory_mapping_high()
Date: Mon, 28 Feb 2011 10:14:44 -0800 [thread overview]
Message-ID: <4D6BE614.3010007@zytor.com> (raw)
In-Reply-To: <20110223171945.GI26065@htj.dyndns.org>
On 02/23/2011 09:19 AM, Tejun Heo wrote:
> Hello, guys.
>
> I've been looking at init_memory_mapping_high() added by commit
> 1411e0ec31 (x86-64, numa: Put pgtable to local node memory) and I got
> curious about several things.
>
> 1. The only rationale given in the commit description is that a
> RED-PEN is killed, which was the following.
>
> /*
> * RED-PEN putting page tables only on node 0 could
> * cause a hotspot and fill up ZONE_DMA. The page tables
> * need roughly 0.5KB per GB.
> */
>
> This already wasn't true with top-down memblock allocation.
>
> The 0.5KB per GiB comment is for 32bit w/ 3 level mapping. On
> 64bit, it's ~4KiB per GiB when using 2MiB mappings and, well, very
> small per GiB if 1GiB mapping is used. Even with 2MiB mapping,
> 1TiB mapping would only be 4MiB. Under ZONE_DMA, this could be
> problematic but with top-down this can't be a problem in any
> realistic way in foreseeable future.
>
It's true on 64 bits too when PAE is not available (e.g. with Xen.)
-hpa
next prev parent reply other threads:[~2011-02-28 18:15 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-02-23 17:19 questions about init_memory_mapping_high() Tejun Heo
2011-02-23 20:24 ` Yinghai Lu
2011-02-23 20:46 ` Tejun Heo
2011-02-23 20:51 ` Yinghai Lu
2011-02-23 21:03 ` Tejun Heo
2011-02-23 22:17 ` Yinghai Lu
2011-02-24 9:15 ` Tejun Heo
2011-02-25 1:37 ` Yinghai Lu
2011-02-25 1:38 ` [PATCH 1/2] x86,mm: Introduce init_memory_mapping_ext() Yinghai Lu
2011-02-25 6:20 ` [PATCH 2/2] x86,mm,64bit: Round up memory boundary for init_memory_mapping_high() Yinghai Lu
2011-02-25 10:03 ` Ingo Molnar
2011-02-25 20:22 ` Yinghai Lu
2011-02-26 3:06 ` [PATCH 1/3] x86, mm: Introduce global page_size_mask Yinghai Lu
2011-02-26 3:07 ` [PATCH 2/3] x86,mm: Introduce init_memory_mapping_ext() Yinghai Lu
2011-02-26 3:08 ` [PATCH 3/3] x86,mm,64bit: Round up memory boundary for init_memory_mapping_high() Yinghai Lu
2011-02-26 10:36 ` Tejun Heo
2011-02-26 10:55 ` Tejun Heo
2011-02-25 11:16 ` [PATCH 2/2] " Tejun Heo
2011-02-25 20:18 ` Yinghai Lu
2011-02-26 8:57 ` Tejun Heo
2011-02-27 11:53 ` Ingo Molnar
2011-02-28 18:14 ` H. Peter Anvin [this message]
2011-03-01 8:29 ` questions about init_memory_mapping_high() Tejun Heo
2011-03-01 19:44 ` H. Peter Anvin
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