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    Subject[PATCH] x86_64: Auto size the per cpu area.
    Date

    Now for a completely different but trivial approach.
    I just boot tested it with 255 CPUS and everything worked.

    Currently everything (except module data) we place in
    the per cpu area we know about at compile time. So
    instead of allocating a fixed size for the per_cpu area
    allocate the number of bytes we need plus a fixed constant
    for to be used for modules.

    It isn't perfect but it is much less of a pain to
    work with than what we are doing now.

    Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
    ---
    arch/x86_64/kernel/setup64.c | 7 ++-----
    include/asm-x86_64/percpu.h | 10 ++++++++++
    2 files changed, 12 insertions(+), 5 deletions(-)

    diff --git a/arch/x86_64/kernel/setup64.c b/arch/x86_64/kernel/setup64.c
    index 0cd3694..94336cf 100644
    --- a/arch/x86_64/kernel/setup64.c
    +++ b/arch/x86_64/kernel/setup64.c
    @@ -95,12 +95,9 @@ #ifdef CONFIG_HOTPLUG_CPU
    #endif

    /* Copy section for each CPU (we discard the original) */
    - size = ALIGN(__per_cpu_end - __per_cpu_start, SMP_CACHE_BYTES);
    -#ifdef CONFIG_MODULES
    - if (size < PERCPU_ENOUGH_ROOM)
    - size = PERCPU_ENOUGH_ROOM;
    -#endif
    + size = PERCPU_ENOUGH_ROOM;

    + printk(KERN_INFO "PERCPU: Allocating %d bytes of per cpu data\n", size);
    for_each_cpu_mask (i, cpu_possible_map) {
    char *ptr;

    diff --git a/include/asm-x86_64/percpu.h b/include/asm-x86_64/percpu.h
    index 08dd9f9..39d2bab 100644
    --- a/include/asm-x86_64/percpu.h
    +++ b/include/asm-x86_64/percpu.h
    @@ -11,6 +11,16 @@ #ifdef CONFIG_SMP

    #include <asm/pda.h>

    +#ifdef CONFIG_MODULES
    +# define PERCPU_MODULE_RESERVE 8192
    +#else
    +# define PERCPU_MODULE_RESERVE 0
    +#endif
    +
    +#define PERCPU_ENOUGH_ROOM \
    + (ALIGN(__per_cpu_end - __per_cpu_start, SMP_CACHE_BYTES) + \
    + PERCPU_MODULE_RESERVE)
    +
    #define __per_cpu_offset(cpu) (cpu_pda(cpu)->data_offset)
    #define __my_cpu_offset() read_pda(data_offset)

    --
    1.4.2.rc3.g7e18e
    -
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