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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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