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    Subject[patch] tlb flush_data: replace per_cpu with an array
    Hi,

    On x86_64 flush tlb data is stored in per_cpu variables. This is
    unnecessary because only the first NUM_INVALIDATE_TLB_VECTORS entries
    are accessed.
    This patch aims at making the code less confusing (there's nothing
    really "per_cpu") by using a plain array. It also would save some memory
    on most distros out there (Ubuntu x86_64 has NR_CPUS=64 by default).

    Regards,
    Frederik

    Signed-off-by: Frederik Deweerdt <frederik.deweerdt@xprog.eu>

    diff --git a/arch/x86/kernel/tlb_64.c b/arch/x86/kernel/tlb_64.c
    index f8be6f1..c177a1f 100644
    --- a/arch/x86/kernel/tlb_64.c
    +++ b/arch/x86/kernel/tlb_64.c
    @@ -33,7 +33,7 @@
    * To avoid global state use 8 different call vectors.
    * Each CPU uses a specific vector to trigger flushes on other
    * CPUs. Depending on the received vector the target CPUs look into
    - * the right per cpu variable for the flush data.
    + * the right array slot for the flush data.
    *
    * With more than 8 CPUs they are hashed to the 8 available
    * vectors. The limited global vector space forces us to this right now.
    @@ -54,7 +54,7 @@ union smp_flush_state {
    /* State is put into the per CPU data section, but padded
    to a full cache line because other CPUs can access it and we don't
    want false sharing in the per cpu data segment. */
    -static DEFINE_PER_CPU(union smp_flush_state, flush_state);
    +static union smp_flush_state flush_state[NUM_INVALIDATE_TLB_VECTORS];

    /*
    * We cannot call mmdrop() because we are in interrupt context,
    @@ -129,7 +129,7 @@ asmlinkage void smp_invalidate_interrupt(struct pt_regs *regs)
    * Use that to determine where the sender put the data.
    */
    sender = ~regs->orig_ax - INVALIDATE_TLB_VECTOR_START;
    - f = &per_cpu(flush_state, sender);
    + f = &flush_state[sender];

    if (!cpu_isset(cpu, f->flush_cpumask))
    goto out;
    @@ -169,7 +169,7 @@ void native_flush_tlb_others(const cpumask_t *cpumaskp, struct mm_struct *mm,

    /* Caller has disabled preemption */
    sender = smp_processor_id() % NUM_INVALIDATE_TLB_VECTORS;
    - f = &per_cpu(flush_state, sender);
    + f = &flush_state[sender];

    /*
    * Could avoid this lock when
    @@ -205,8 +205,8 @@ static int __cpuinit init_smp_flush(void)
    {
    int i;

    - for_each_possible_cpu(i)
    - spin_lock_init(&per_cpu(flush_state, i).tlbstate_lock);
    + for (i = 0; i < ARRAY_SIZE(flush_state); i++)
    + spin_lock_init(&flush_state[i].tlbstate_lock);

    return 0;
    }

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