linux-kernel - Re: [PATCH] x86-64: improve e820_search

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Date:	Thu, 12 Mar 2009 12:02:44 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Jan Beulich <jbeulich@...ell.com>, Yinghai Lu <yinghai@...nel.org>
Cc:	tglx@...utronix.de, hpa@...or.com, jeremy.fitzhardinge@...rix.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86-64: improve e820_search_gap()


* Jan Beulich <jbeulich@...ell.com> wrote:

> Blindly putting the gap close after max_pfn might be fine for native
> (though even there I'm uncertain regarding memory hotplug), but will
> certainly present a problem on Xen. And properly searching for a gap
> above 4Gb shouldn't hurt native.
> 
> Also, make the function static to ensure there are no other users that
> could depend on the previous behavior regarding the way start_addr gets
> specified.
> 
> Signed-off-by: Jan Beulich <jbeulich@...ell.com>
> Cc: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
> 
> ---
>  arch/x86/include/asm/e820.h |    2 --
>  arch/x86/kernel/e820.c      |   11 +++++++++--
>  2 files changed, 9 insertions(+), 4 deletions(-)
> 
> --- linux-2.6.29-rc7/arch/x86/include/asm/e820.h	2009-03-11 17:52:10.000000000 +0100
> +++ 2.6.29-rc7-x86_64-e820-setup-gap-64bit/arch/x86/include/asm/e820.h	2009-03-06 11:25:35.000000000 +0100
> @@ -79,8 +79,6 @@ extern u64 e820_remove_range(u64 start, 
>  			     int checktype);
>  extern void update_e820(void);
>  extern void e820_setup_gap(void);
> -extern int e820_search_gap(unsigned long *gapstart, unsigned long *gapsize,
> -			unsigned long start_addr, unsigned long long end_addr);
>  struct setup_data;
>  extern void parse_e820_ext(struct setup_data *data, unsigned long pa_data);
>  
> --- linux-2.6.29-rc7/arch/x86/kernel/e820.c	2009-03-11 17:52:10.000000000 +0100
> +++ 2.6.29-rc7-x86_64-e820-setup-gap-64bit/arch/x86/kernel/e820.c	2009-03-06 11:24:34.000000000 +0100
> @@ -533,13 +533,19 @@ static void __init update_e820_saved(voi
>  /*
>   * Search for a gap in the e820 memory space from start_addr to end_addr.
>   */
> -__init int e820_search_gap(unsigned long *gapstart, unsigned long *gapsize,
> +static int __init
> +e820_search_gap(unsigned long *gapstart, unsigned long *gapsize,
>  		unsigned long start_addr, unsigned long long end_addr)
>  {
>  	unsigned long long last;
>  	int i = e820.nr_map;
>  	int found = 0;
>  
> +#ifdef CONFIG_X86_64
> +	if (start_addr >= MAX_GAP_END)
> +		last = end_addr ?: (1UL << boot_cpu_data.x86_phys_bits);
> +	else
> +#endif
>  	last = (end_addr && end_addr < MAX_GAP_END) ? end_addr : MAX_GAP_END;

hm, this #ifdef block looks quite ugly and should be cleaned up. 
x86_phys_bits could be filled in on 32-bit too - and on 32-bit 
start_addr cannot be larger than 4GB anyway.

>  	while (--i >= 0) {
> @@ -585,11 +591,12 @@ __init void e820_setup_gap(void)
>  
>  #ifdef CONFIG_X86_64
>  	if (!found) {
> -		gapstart = (max_pfn << PAGE_SHIFT) + 1024*1024;
>  		printk(KERN_ERR "PCI: Warning: Cannot find a gap in the 32bit "
>  		       "address range\n"
>  		       KERN_ERR "PCI: Unassigned devices with 32bit resource "
>  		       "registers may break!\n");
> +		found = e820_search_gap(&gapstart, &gapsize, MAX_GAP_END, 0);
> +		BUG_ON(!found);

that BUG_ON() will be hard to debug - please use a WARN_ON 
instead.

	Ingo
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