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    Subject[PATCH 03/14] x86, config: change defaults PHYSICAL_START and PHYSICAL_ALIGN
    Date
    From: H. Peter Anvin <hpa@zytor.com>

    Change the default for CONFIG_PHYSICAL_START to 16 MB; 4 MB if
    EMBEDDED. Change the default for CONFIG_PHYSICAL_ALIGN to match up
    with a large page alignment datum (4 MB for non-PAE, 2 MB for PAE.)

    The default of 16 MB is designed to avoid occupying ZONE_DMA, as well
    as avoiding a 15-16 MB memory hole, which some vendors inexplicably
    still have in their systems.

    [ Impact: minor performance improvement, leave ZONE_DMA free ]

    Signed-off-by: H. Peter Anvin <hpa@zytor.com>
    ---
    arch/x86/Kconfig | 19 +++++++++++--------
    1 files changed, 11 insertions(+), 8 deletions(-)

    diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
    index 039c3f0..13b3a5a 100644
    --- a/arch/x86/Kconfig
    +++ b/arch/x86/Kconfig
    @@ -1455,17 +1455,20 @@ config KEXEC_JUMP

    config PHYSICAL_START
    hex "Physical address where the kernel is loaded" if (EMBEDDED || CRASH_DUMP)
    - default "0x1000000" if X86_NUMAQ
    - default "0x200000" if X86_64
    - default "0x100000"
    + default "0x400000" if EMBEDDED
    + default "0x1000000"
    ---help---
    This gives the physical address where the kernel is loaded.

    If kernel is a not relocatable (CONFIG_RELOCATABLE=n) then
    bzImage will decompress itself to above physical address and
    - run from there. Otherwise, bzImage will run from the address where
    - it has been loaded by the boot loader and will ignore above physical
    - address.
    + run from there. Otherwise, bzImage will run from the either
    + the above physical address or where it has been loaded by
    + the boot loader, whichever is higher.
    +
    + For embedded machines with very small memory (less than
    + about 24 MB) this may need to be adjusted downward from the
    + default value of 0x1000000 (16 MB).

    In normal kdump cases one does not have to set/change this option
    as now bzImage can be compiled as a completely relocatable image
    @@ -1516,8 +1519,8 @@ config RELOCATABLE
    config PHYSICAL_ALIGN
    hex
    prompt "Alignment value to which kernel should be aligned" if X86_32
    - default "0x100000" if X86_32
    - default "0x200000" if X86_64
    + default "0x200000" if X86_64 || X86_PAE
    + default "0x400000"
    range 0x2000 0x400000
    ---help---
    This value puts the alignment restrictions on physical address
    --
    1.6.0.6


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