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

[Jeremy Fitzhardinge]

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
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