Re: [GIT PULL] x86: add brk allocator for very early allocations

[Jeremy Fitzhardinge <jeremy@goop.org>]

Yinghai Lu wrote:
> Jeremy Fitzhardinge wrote:
>   
>> H. Peter Anvin wrote:
>>     
>>> Those references are just the actual reservation of memory.  If all
>>> the users of that memory are converted to either brk or bss,
>>> INIT_MAP_BEYOND_END should be removed.  If all the users of that
>>> memory aren't converted to brk to bss, we should do so.
>>>       
>> I just added an adapted Yinghai's patch and added it to push/x86/brk.
>>
>>    J
>>
>>
>> The following changes since commit
>> 8131667360004a0b74e4dcadfee8a18d4e2b074f:
>>  Jeremy Fitzhardinge (1):
>>        x86: allow extend_brk users to reserve brk space
>>
>> are available in the git repository at:
>>
>>  git://git.kernel.org/pub/scm/linux/kernel/git/jeremy/xen.git push/x86/brk
>>
>> Yinghai Lu (1):
>>      x86: put initial_pg_tables into .bss -v4
>>
>> arch/x86/kernel/head_32.S        |   47
>> ++++++++++++++-----------------------
>> arch/x86/kernel/vmlinux_32.lds.S |    6 +++++
>> 2 files changed, 24 insertions(+), 29 deletions(-)
>>
>> diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
>> index 80dc05e..ad7dbbb 100644
>> --- a/arch/x86/kernel/head_32.S
>> +++ b/arch/x86/kernel/head_32.S
>> @@ -38,42 +38,30 @@
>> #define X86_VENDOR_ID    new_cpu_data+CPUINFO_x86_vendor_id
>>
>> /*
>> - * This is how much memory *in addition to the memory covered up to
>> - * and including _end* we need mapped initially.
>> - * We need:
>> - *  - one bit for each possible page, but only in low memory, which means
>> - *     2^32/4096/8 = 128K worst case (4G/4G split.)
>> + * This is how much memory for page table to and including _end
>> + * we need mapped initially.
>>  *  - enough space to map all low memory, which means
>> - *     (2^32/4096) / 1024 pages (worst case, non PAE)
>> - *     (2^32/4096) / 512 + 4 pages (worst case for PAE)
>> - *  - a few pages for allocator use before the kernel pagetable has
>> - *     been set up
>> + *     (KERNEL_IMAGE_SIZE/4096) / 1024 pages (worst case, non PAE)
>> + *     (KERNEL_IMAGE_SIZE/4096) / 512 + 4 pages (worst case for PAE)
>>  *
>>  * Modulo rounding, each megabyte assigned here requires a kilobyte of
>>  * memory, which is currently unreclaimed.
>>  *
>>  * This should be a multiple of a page.
>> + *
>> + * KERNEL_IMAGE_SIZE should be greater than pa(_end)
>> + * and small than max_low_pfn, otherwise will waste some page table
>> entries
>>  */
>> LOW_PAGES = (KERNEL_IMAGE_SIZE + PAGE_SIZE_asm - 1)>>PAGE_SHIFT
>>
>> -/*
>> - * To preserve the DMA pool in PAGEALLOC kernels, we'll allocate
>> - * pagetables from above the 16MB DMA limit, so we'll have to set
>> - * up pagetables 16MB more (worst-case):
>> - */
>> -#if defined(CONFIG_DEBUG_PAGEALLOC) || defined(CONFIG_KMEMCHECK)
>> -LOW_PAGES = LOW_PAGES + 0x1000000
>> -#endif
>> -
>> #if PTRS_PER_PMD > 1
>> PAGE_TABLE_SIZE = (LOW_PAGES / PTRS_PER_PMD) + PTRS_PER_PGD
>> #else
>> PAGE_TABLE_SIZE = (LOW_PAGES / PTRS_PER_PGD)
>> #endif
>> -BOOTBITMAP_SIZE = LOW_PAGES / 8
>> ALLOCATOR_SLOP = 4
>>
>> -INIT_MAP_BEYOND_END = BOOTBITMAP_SIZE + (PAGE_TABLE_SIZE +
>> ALLOCATOR_SLOP)*PAGE_SIZE_asm
>> +INIT_MAP_SIZE = (PAGE_TABLE_SIZE + ALLOCATOR_SLOP) * PAGE_SIZE_asm
>>
>> RESERVE_BRK(pagetables, PAGE_TABLE_SIZE * PAGE_SIZE)
>>     
>
> use INIT_MAP_SIZE in RESERVE_BRK directly?
>   
OK.

>   
>> @@ -168,10 +156,10 @@ num_subarch_entries = (. - subarch_entries) / 4
>>
>> /*
>>  * Initialize page tables.  This creates a PDE and a set of page
>> - * tables, which are located immediately beyond _end.  The variable
>> + * tables, which are located immediately beyond __brk_base.  The variable
>>  * _brk_end is set up to point to the first "safe" location.
>>  * Mappings are created both at virtual address 0 (identity mapping)
>> - * and PAGE_OFFSET for up to _end+sizeof(page tables)+INIT_MAP_BEYOND_END.
>> + * and PAGE_OFFSET for up to _end.
>>  *
>>  * Note that the stack is not yet set up!
>>  */
>> @@ -210,10 +198,9 @@ default_entry:
>>     loop 11b
>>
>>     /*
>> -     * End condition: we must map up to and including INIT_MAP_BEYOND_END
>> -     * bytes beyond the end of our own page tables.
>> +     * End condition: we must map up to the end.
>>      */
>> -    leal (INIT_MAP_BEYOND_END+PTE_IDENT_ATTR)(%edi),%ebp
>> +    movl $pa(_end) + PTE_IDENT_ATTR, %ebp
>>     cmpl %ebp,%eax
>>     jb 10b
>> 1:
>> @@ -243,11 +230,9 @@ page_pde_offset = (__PAGE_OFFSET >> 20);
>>     addl $0x1000,%eax
>>     loop 11b
>>     /*
>> -     * End condition: we must map up to and including INIT_MAP_BEYOND_END
>> -     * bytes beyond the end of our own page tables; the +0x007 is
>> -     * the attribute bits
>> +     * End condition: we must map up to end
>>      */
>> -    leal (INIT_MAP_BEYOND_END+PTE_IDENT_ATTR)(%edi),%ebp
>> +    movl $pa(_end) + PTE_IDENT_ATTR, %ebp
>>     cmpl %ebp,%eax
>>     jb 10b
>>     addl $__PAGE_OFFSET, %edi
>> @@ -638,6 +623,10 @@ swapper_pg_fixmap:
>>     .fill 1024,4,0
>> ENTRY(empty_zero_page)
>>     .fill 4096,1,0
>> +
>> +.section ".bss.extra_page_aligned","wa"
>> +    .align PAGE_SIZE_asm
>> +    .fill INIT_MAP_SIZE,1,0
>>     
>
> this 4 lines are not needed. you already had RESERVE_BRK for it.
>
>   

OK.

I've updated the changeset and repushed.

    J