linux-kernel - Re: [PATCH] [0/31] Great change_page

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Message-Id: <478CAD42.76E4.0078.0@novell.com>
Date:	Tue, 15 Jan 2008 11:55:30 +0000
From:	"Jan Beulich" <jbeulich@...ell.com>
To:	"Andi Kleen" <ak@...e.de>
Cc:	<mingo@...e.hu>, <tglx@...utronix.de>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] [0/31] Great change_page_attr patch series v2

>> The one concept that I'm missing (but that I can easily produce a follow-up
>> patch for, as I had this in my c_p_a() changes) is the tracking and adjusting
>> of the reference protection for a large page range that got fully converted
>> to another type (namely relevant for .rodata if it exceeds 2/4 Mb), allowing
>> to use a large page mapping in this case even for non-default mappings.
>
>Ah -- i got rid of that by changing the rodata code to not do this
>except for the debugging case
>
>>>
>CPA: Only unmap kernel init pages in text mapping when CONFIG_DEBUG_RODATA is set
>
>Otherwise the kernel will likely always run with 4K pages instead of 2MB pages,
>which is costly in terms of TLBs.
><<
>
>But you're right that would be an useful feature. But wouldn't it require
>aligning rodata to 2MB in the vmlinux to be really effective? 

Yes, that would be desirable then (and .data should be at a 2/4 Mb
boundary for this, too).

Jan

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