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From: Yinghai Lu <yinghai@kernel.org>
To: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>,
	"H. Peter Anvin" <hpa@zytor.com>, Jacob Shin <jacob.shin@amd.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Stefano Stabellini <stefano.stabellini@eu.citrix.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v8 21/46] x86, mm: setup page table in top-down
Date: Wed, 28 Nov 2012 12:16:16 -0800
Message-ID: <CAE9FiQWVL3mq7dCP1g_euK_7PK2gUE+1XXNoZPsqt+wnFdtFhw@mail.gmail.com> (raw)
In-Reply-To: <20121128175007.GN21266@phenom.dumpdata.com>

On Wed, Nov 28, 2012 at 9:50 AM, Konrad Rzeszutek Wilk
<konrad.wilk@oracle.com> wrote:
>>  /*
>> - * Iterate through E820 memory map and create direct mappings for only E820_RAM
>> - * regions. We cannot simply create direct mappings for all pfns from
>> - * [0 to max_low_pfn) and [4GB to max_pfn) because of possible memory holes in
>> - * high addresses that cannot be marked as UC by fixed/variable range MTRRs.
>> - * Depending on the alignment of E820 ranges, this may possibly result in using
>> - * smaller size (i.e. 4K instead of 2M or 1G) page tables.
>> + * would have hole in the middle or ends, and only ram parts will be mapped.
>
>
> What? What is the 'would' refering to? Why remove a good comment that explains
> the function. Why not just modify it a bit please?
>

==> update to

/*
 * We need to iterate through E820 memory map and create direct mappings
 * for only E820_RAM and E820_KERN_RESERVED regions. We cannot simply
 * create direct mappings for all pfns from [0 to max_low_pfn) and
 * [4GB to max_pfn) because of possible memory holes in high addresses
 * that cannot be marked as UC by fixed/variable range MTRRs.
 * Depending on the alignment of E820 ranges, this may possibly result
 * in using smaller size (i.e. 4K instead of 2M or 1G) page tables.
 *
 * init_mem_mapping call init_range_memory_mapping with big range.
 * That range would have hole in the middle or ends, and only ram parts
 * will be mapped in init_range_memory_mapping.
 */



>> -     max_pfn_mapped = 0; /* will get exact value next */
>>       /* the ISA range is always mapped regardless of memory holes */
>>       init_memory_mapping(0, ISA_END_ADDRESS);
>> -     init_range_memory_mapping(ISA_END_ADDRESS, end);
>> +
>> +     /* xen has big range in reserved near end of ram, skip it at first */
>
> I am not seeing the logic for doing it? The loop is quite generic
> in doing it in reverse order, and the memblock_find_in_range
> gets a nice PMD_SIZE region from the end of the memory.
>
> If the memory at the end is reserved, then it looks like it won't
> be even considered in the loop, but it does get included in the fallback:
>
>         if (real_end < end)
>                 init_range_memory_mapping(real_end, end);

that reserved in in memblock.reserved and it is not in e820.

so memblock.memory will have that range too. then if we use all of
first 2M to map

those reserved range, we would not have enough mapped pages to be used
as new page tables.

>
>
>
>> +     addr = memblock_find_in_range(ISA_END_ADDRESS, end, PMD_SIZE,
>> +                      PAGE_SIZE);
>> +     real_end = addr + PMD_SIZE;
>> +
>> +     /* step_size need to be small so pgt_buf from BRK could cover it */
>> +     step_size = PMD_SIZE;
>> +     max_pfn_mapped = 0; /* will get exact value next */
>> +     min_pfn_mapped = real_end >> PAGE_SHIFT;
>> +     last_start = start = real_end;
>
> Everytime I look at this loop, I keep on forgetting that it goes in reverse.
> I am not sure if it is just me, but it might be useful for other
> folks who are going to look at this in a year or so to have
> a little hint:
>
> N.B. We start from the top (end of memory) and go to the bottom. The
> memblock_find_in_range gets us a block of RAM from the end
> of RAM.

put the that in the comments.

  reply index

Thread overview: 119+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-11-17  3:38 [PATCH v8 00/46] x86, mm: map ram from top-down with BRK and memblock Yinghai Lu
2012-11-17  3:38 ` [PATCH v8 01/46] x86, mm: Add global page_size_mask and probe one time only Yinghai Lu
2012-11-22  1:38   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-17  3:38 ` [PATCH v8 02/46] x86, mm: Split out split_mem_range from init_memory_mapping Yinghai Lu
2012-11-22  1:39   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-17  3:38 ` [PATCH v8 03/46] x86, mm: Move down find_early_table_space() Yinghai Lu
2012-11-22  1:40   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-28 16:50   ` [PATCH v8 03/46] " Konrad Rzeszutek Wilk
2012-11-17  3:38 ` [PATCH v8 04/46] x86, mm: Move init_memory_mapping calling out of setup.c Yinghai Lu
2012-11-22  1:41   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-28 16:50   ` [PATCH v8 04/46] " Konrad Rzeszutek Wilk
2012-11-17  3:38 ` [PATCH v8 05/46] x86, mm: Revert back good_end setting for 64bit Yinghai Lu
2012-11-22  1:42   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-17  3:38 ` [PATCH v8 06/46] x86, mm: Change find_early_table_space() paramters Yinghai Lu
2012-11-22  1:43   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-28 16:50   ` [PATCH v8 06/46] " Konrad Rzeszutek Wilk
2012-11-17  3:38 ` [PATCH v8 07/46] x86, mm: Find early page table buffer together Yinghai Lu
2012-11-22  1:44   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-28 16:50   ` [PATCH v8 07/46] " Konrad Rzeszutek Wilk
2012-11-17  3:38 ` [PATCH v8 08/46] x86, mm: Separate out calculate_table_space_size() Yinghai Lu
2012-11-22  1:45   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-28 16:59   ` [PATCH v8 08/46] " Konrad Rzeszutek Wilk
2012-11-17  3:38 ` [PATCH v8 09/46] x86, mm: Set memblock initial limit to 1M Yinghai Lu
2012-11-22  1:46   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-17  3:38 ` [PATCH v8 10/46] x86, mm: if kernel .text .data .bss are not marked as E820_RAM, complain and fix Yinghai Lu
2012-11-22  1:47   ` [tip:x86/mm2] " tip-bot for Jacob Shin
2012-11-17  3:38 ` [PATCH v8 11/46] x86, mm: Fixup code testing if a pfn is direct mapped Yinghai Lu
2012-11-22  1:48   ` [tip:x86/mm2] " tip-bot for Jacob Shin
2012-11-17  3:38 ` [PATCH v8 12/46] x86, mm: use pfn_range_is_mapped() with CPA Yinghai Lu
2012-11-22  1:49   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-28 17:06   ` [PATCH v8 12/46] " Konrad Rzeszutek Wilk
2012-11-28 19:33     ` Yinghai Lu
2012-11-17  3:38 ` [PATCH v8 13/46] x86, mm: use pfn_range_is_mapped() with gart Yinghai Lu
2012-11-22  1:50   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-28 17:07   ` [PATCH v8 13/46] " Konrad Rzeszutek Wilk
2012-11-17  3:38 ` [PATCH v8 14/46] x86, mm: use pfn_range_is_mapped() with reserve_initrd Yinghai Lu
2012-11-22  1:51   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-28 17:08   ` [PATCH v8 14/46] " Konrad Rzeszutek Wilk
2012-11-28 19:40     ` Yinghai Lu
2012-11-17  3:38 ` [PATCH v8 15/46] x86, mm: Only direct map addresses that are marked as E820_RAM Yinghai Lu
2012-11-22  1:53   ` [tip:x86/mm2] " tip-bot for Jacob Shin
2012-11-28 17:15   ` [PATCH v8 15/46] " Konrad Rzeszutek Wilk
2012-11-28 19:43     ` Yinghai Lu
2012-11-17  3:38 ` [PATCH v8 16/46] x86, mm: relocate initrd under all mem for 64bit Yinghai Lu
2012-11-22  1:54   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-17  3:38 ` [PATCH v8 17/46] x86, mm: Align start address to correct big page size Yinghai Lu
2012-11-22  1:55   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-17  3:38 ` [PATCH v8 18/46] x86, mm: Use big page size for small memory range Yinghai Lu
2012-11-22  1:56   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-17  3:38 ` [PATCH v8 19/46] x86, mm: Don't clear page table if range is ram Yinghai Lu
2012-11-22  1:57   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-17  3:38 ` [PATCH v8 20/46] x86, mm: Break down init_all_memory_mapping Yinghai Lu
2012-11-22  1:58   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-17  3:38 ` [PATCH v8 21/46] x86, mm: setup page table in top-down Yinghai Lu
2012-11-22  1:59   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-28 17:50   ` [PATCH v8 21/46] " Konrad Rzeszutek Wilk
2012-11-28 20:16     ` Yinghai Lu [this message]
2012-12-05 21:53       ` Konrad Rzeszutek Wilk
2012-11-17  3:38 ` [PATCH v8 22/46] x86, mm: Remove early_memremap workaround for page table accessing on 64bit Yinghai Lu
2012-11-22  2:00   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-28 18:57   ` [PATCH v8 22/46] " Konrad Rzeszutek Wilk
2012-11-17  3:39 ` [PATCH v8 23/46] x86, mm: Remove parameter in alloc_low_page for 64bit Yinghai Lu
2012-11-22  2:01   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-28 18:57   ` [PATCH v8 23/46] " Konrad Rzeszutek Wilk
2012-11-17  3:39 ` [PATCH v8 24/46] x86, mm: Merge alloc_low_page between 64bit and 32bit Yinghai Lu
2012-11-22  2:02   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-17  3:39 ` [PATCH v8 25/46] x86, mm: Move min_pfn_mapped back to mm/init.c Yinghai Lu
2012-11-22  2:03   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-17  3:39 ` [PATCH v8 26/46] x86, mm, Xen: Remove mapping_pagetable_reserve() Yinghai Lu
2012-11-22  2:04   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-17  3:39 ` [PATCH v8 27/46] x86, mm: Add alloc_low_pages(num) Yinghai Lu
2012-11-22  2:05   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-17  3:39 ` [PATCH v8 28/46] x86, mm: Add pointer about Xen mmu requirement for alloc_low_pages Yinghai Lu
2012-11-22  2:06   ` [tip:x86/mm2] " tip-bot for Stefano Stabellini
2012-11-17  3:39 ` [PATCH v8 29/46] x86, mm: only call early_ioremap_page_table_range_init() once Yinghai Lu
2012-11-22  2:07   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-28 19:02   ` [PATCH v8 29/46] " Konrad Rzeszutek Wilk
2012-11-17  3:39 ` [PATCH v8 30/46] x86, mm: Move back pgt_buf_* to mm/init.c Yinghai Lu
2012-11-22  2:08   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-17  3:39 ` [PATCH v8 31/46] x86, mm: Move init_gbpages() out of setup.c Yinghai Lu
2012-11-22  2:09   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-17  3:39 ` [PATCH v8 32/46] x86, mm: change low/hignmem_pfn_init to static on 32bit Yinghai Lu
2012-11-22  2:10   ` [tip:x86/mm2] x86, mm: change low/ hignmem_pfn_init " tip-bot for Yinghai Lu
2012-11-17  3:39 ` [PATCH v8 33/46] x86, mm: Move function declaration into mm_internal.h Yinghai Lu
2012-11-22  2:11   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-17  3:39 ` [PATCH v8 34/46] x86, mm: Add check before clear pte above max_low_pfn on 32bit Yinghai Lu
2012-11-22  2:13   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-28 19:09   ` [PATCH v8 34/46] " Konrad Rzeszutek Wilk
2012-11-28 20:38     ` Yinghai Lu
2012-11-17  3:39 ` [PATCH v8 35/46] x86, mm: use round_up/down in split_mem_range() Yinghai Lu
2012-11-22  2:14   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-17  3:39 ` [PATCH v8 36/46] x86, mm: use PFN_DOWN " Yinghai Lu
2012-11-22  2:15   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-17  3:39 ` [PATCH v8 37/46] x86, mm: use pfn instead of pos in split_mem_range Yinghai Lu
2012-11-22  2:16   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-17  3:39 ` [PATCH v8 38/46] x86, mm: use limit_pfn for end pfn Yinghai Lu
2012-11-22  2:17   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-17  3:39 ` [PATCH v8 39/46] x86, mm: Unifying after_bootmem for 32bit and 64bit Yinghai Lu
2012-11-22  2:18   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-17  3:39 ` [PATCH v8 40/46] x86, mm: Move after_bootmem to mm_internel.h Yinghai Lu
2012-11-22  2:19   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-17  3:39 ` [PATCH v8 41/46] x86, mm: Use clamp_t() in init_range_memory_mapping Yinghai Lu
2012-11-22  2:20   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-17  3:39 ` [PATCH v8 42/46] x86, mm: kill numa_free_all_bootmem() Yinghai Lu
2012-11-22  2:21   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-17  3:39 ` [PATCH v8 43/46] x86, mm: kill numa_64.h Yinghai Lu
2012-11-22  2:22   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-17  3:39 ` [PATCH v8 44/46] sparc, mm: Remove calling of free_all_bootmem_node() Yinghai Lu
2012-11-22  2:23   ` [tip:x86/mm2] sparc, mm: Remove calling of free_all_bootmem_node( ) tip-bot for Yinghai Lu
2012-11-17  3:39 ` [PATCH v8 45/46] mm: Kill NO_BOOTMEM version free_all_bootmem_node() Yinghai Lu
2012-11-22  2:24   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-17  3:39 ` [PATCH v8 46/46] x86, mm: Let "memmap=" take more entries one time Yinghai Lu
2012-11-22  2:25   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2012-11-28 19:12   ` [PATCH v8 46/46] " Konrad Rzeszutek Wilk
2012-11-27 21:17 ` [PATCH v8 00/46] x86, mm: map ram from top-down with BRK and memblock Konrad Rzeszutek Wilk
2012-11-28 19:35   ` Konrad Rzeszutek Wilk
2012-11-28 19:47     ` Yinghai Lu
2012-11-28 20:57       ` Konrad Rzeszutek Wilk
2012-11-28 21:06         ` Yinghai Lu

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