linux-kernel - Re: [PATCH -v2 13/13] x86, 64bit: Map first 1M ram early before memblock_x86

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Date:	Sun, 2 Sep 2012 23:17:18 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	Pekka Enberg <penberg@...nel.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>,
	"H. Peter Anvin" <hpa@...or.com>, Jacob Shin <jacob.shin@....com>,
	Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -v2 13/13] x86, 64bit: Map first 1M ram early before memblock_x86_fill()

On Sun, Sep 2, 2012 at 10:50 PM, Pekka Enberg <penberg@...nel.org> wrote:
> On Sun, Sep 2, 2012 at 10:46 AM, Yinghai Lu <yinghai@...nel.org> wrote:
>> This one intend to fix bugs:
>> when efi booting have too many memmap entries, will need to double memblock
>> memory array or reserved array.
>
> Okay, why do we need to do that?

memblock initial memory only have 128 entry, and some EFI system could
have more entries than that.

So during memblock_x86_fill need to double that array.

and efi_reserve_boot_services() could make thing more worse. aka need
more entries in memblock.memory.regions.

>
>> +RESERVE_BRK(early_pgt_alloc, 65536);
>
> What is this needed for?

for extra page table, and extend_brk will consume that.

>
>> +void  __init early_init_mem_mapping(void)
>> +{
>> +       unsigned long tables;
>> +       phys_addr_t base;
>> +       unsigned long start = 0, end = ISA_END_ADDRESS;
>> +
>> +       probe_page_size_mask();
>> +
>> +       if (max_pfn_mapped)
>> +               return;
>
> I find this confusing - what is this protecting for? Why is
> 'max_pfn_mapped' set when someone calls early_init_mem_mappings()?

for 32 bit, it will non zero max_pfn_mapped set in head_32.S

>
> Side note: we have multiple "pfn_mapped" globals and it's not at all
> obvious to me what the semantics for them are. Maybe adding a comment
> or two in arch/x86/include/asm/page_types.h would help.

move the comments  from arch/x86/kernel/setup.c to that header file ?

Thanks

Yinghai
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