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From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
To: Yinghai Lu <yinghai@kernel.org>
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, 5 Dec 2012 16:53:08 -0500
Message-ID: <20121205215308.GB1284@phenom.dumpdata.com> (raw)
In-Reply-To: <CAE9FiQWVL3mq7dCP1g_euK_7PK2gUE+1XXNoZPsqt+wnFdtFhw@mail.gmail.com>

On Wed, Nov 28, 2012 at 12:16:16PM -0800, Yinghai Lu wrote:
> 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.

You should include that nice explanation as part of the comment. It is
rather suddle (or would be for me in 6 months when I would look at this
code).

> 
> >
> >
> >
> >> +     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
2012-12-05 21:53       ` Konrad Rzeszutek Wilk [this message]
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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