linux-kernel - Re: [PATCH 1/5] x86: Only direct map addresses that are marked as E820

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Message-ID: <20120811194948.GC2874@dhcp-172-17-108-109.mtv.corp.google.com>
Date:	Sat, 11 Aug 2012 12:49:48 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Jacob Shin <jacob.shin@....com>
Cc:	X86-ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
	Yinghai Lu <yinghai@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andreas Herrmann <andreas.herrmann3@....com>
Subject: Re: [PATCH 1/5] x86: Only direct map addresses that are marked as
 E820_RAM

Hello, Jacob.

On Thu, Aug 09, 2012 at 04:23:05PM -0500, Jacob Shin wrote:
> +struct range pfn_mapped[E820_X_MAX];
> +int nr_pfn_mapped;

Why aren't these __initdata?  Are they gonna be used for other
purposes?

> +void add_pfn_range_mapped(unsigned long start_pfn, unsigned long end_pfn)
> +{
> +	nr_pfn_mapped = add_range_with_merge(pfn_mapped, E820_X_MAX,
> +					     nr_pfn_mapped, start_pfn, end_pfn);
> +
> +	if (end_pfn > max_pfn_mapped)
> +		max_pfn_mapped = end_pfn;

Maybe use max()?

> +	if ((end_pfn <= (1UL << (32 - PAGE_SHIFT))) &&
> +	    (end_pfn > max_low_pfn_mapped))
> +		max_low_pfn_mapped = end_pfn;
> +}
> +
> +int pfn_range_is_mapped(unsigned long start_pfn, unsigned long end_pfn)

bool?

> +{
> +	int i;
> +
> +	for (i = 0; i < nr_pfn_mapped; i++)
> +		if ((start_pfn >= pfn_mapped[i].start) &&
> +		    (end_pfn <= pfn_mapped[i].end))
> +			break;
> +
> +	return i < nr_pfn_mapped;
> +}

	for (...)
		if (xxx)
			return true;
	return false;

> +int pfn_is_mapped(unsigned long pfn)
> +{
> +	int i;
> +
> +	for (i = 0; i < nr_pfn_mapped; i++)
> +		if ((pfn >= pfn_mapped[i].start) &&
> +		    (pfn <  pfn_mapped[i].end))
> +			break;
> +
> +	return i < nr_pfn_mapped;
> +}

How about...

	return pfn_range_is_mapped(pfn, pfn + 1);

> @@ -913,14 +958,40 @@ void __init setup_arch(char **cmdline_p)
>  
>  	init_gbpages();
>  
> -	/* max_pfn_mapped is updated here */
> -	max_low_pfn_mapped = init_memory_mapping(0, max_low_pfn<<PAGE_SHIFT);
> -	max_pfn_mapped = max_low_pfn_mapped;
> +	init_pfn = max_pfn_mapped;
> +
> +	memset(pfn_mapped, 0, sizeof(pfn_mapped));
> +	nr_pfn_mapped = 0;

Are these necessary?  We clear .bss way before control reaches here.

> +
> +	add_pfn_range_mapped(0, max_pfn_mapped);
> +
> +	for (i = 0; i < e820.nr_map; i++) {
> +		struct e820entry *ei = &e820.map[i];
> +		u64 start = ei->addr;
> +		u64 end = ei->addr + ei->size;
> +
> +		if (ei->type != E820_RAM)
> +			continue;
> +
> +		if (end <= (init_pfn << PAGE_SHIFT))
> +			continue;
> +
> +		if (start < (init_pfn << PAGE_SHIFT))
> +			start = init_pfn << PAGE_SHIFT;
> +
> +#ifdef CONFIG_X86_32
> +		if ((start >> PAGE_SHIFT) >= max_low_pfn)
> +			continue;
> +
> +		if ((end >> PAGE_SHIFT) > max_low_pfn)
> +			end = max_low_pfn << PAGE_SHIFT;
> +#endif
> +		pfn = init_memory_mapping(start, end);
> +		add_pfn_range_mapped(start >> PAGE_SHIFT, pfn);
> +	}

Some comments please?  Also, while this may be the right thing to do,
if I'm not mistaken, this is also likely to make linear space to use
smaller mappings depending on how the physical memory is laid out,
which could be a trade off we're willing to make, but that *should* be
explicit.  Please describe what's going on and provide rationale.

Thanks.

-- 
tejun
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