Re: [PATCH v5 6/7] x86/tlb: optimizing flush_tlb_mm

[Alex Shi]

On 05/16/2012 04:00 PM, Peter Zijlstra wrote:

> On Wed, 2012-05-16 at 14:46 +0800, Alex Shi wrote:
>> diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h
>> index 75e888b..ed6642a 100644
>> --- a/include/asm-generic/tlb.h
>> +++ b/include/asm-generic/tlb.h
>> @@ -86,6 +86,8 @@ struct mmu_gather {
>>  #ifdef CONFIG_HAVE_RCU_TABLE_FREE
>>         struct mmu_table_batch  *batch;
>>  #endif
>> +       unsigned long           start;
>> +       unsigned long           end;
>>         unsigned int            need_flush : 1, /* Did free PTEs */
>>                                 fast_mode  : 1; /* No batching   */
>>  
>> diff --git a/mm/memory.c b/mm/memory.c
>> index 6105f47..b176172 100644
>> --- a/mm/memory.c
>> +++ b/mm/memory.c
>> @@ -206,6 +206,8 @@ void tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm, bool fullmm)
>>         tlb->mm = mm;
>>  
>>         tlb->fullmm     = fullmm;
>> +       tlb->start      = -1UL;
>> +       tlb->end        = 0;
>>         tlb->need_flush = 0;
>>         tlb->fast_mode  = (num_possible_cpus() == 1);
>>         tlb->local.next = NULL;
>> @@ -248,6 +250,8 @@ void tlb_finish_mmu(struct mmu_gather *tlb, unsigned long start, unsigned long e
>>  {
>>         struct mmu_gather_batch *batch, *next;
>>  
>> +       tlb->start = start;
>> +       tlb->end   = end;
>>         tlb_flush_mmu(tlb);
>>  
>>         /* keep the page table cache within bounds */
>> @@ -1204,6 +1208,8 @@ again:
>>          */
>>         if (force_flush) {
>>                 force_flush = 0;
>> +               tlb->start = addr;
>> +               tlb->end = end;
>>                 tlb_flush_mmu(tlb);
>>                 if (addr != end)
>>                         goto again; 
> 
> 
> ARGH.. no. What bit about you don't need to modify the generic code
> don't you get?
> 
> Both ARM and IA64 (and possible others) already do range tracking, you
> don't need to modify mm/memory.c _AT_ALL_.



Thanks for time and time remdiner. (shame for me)

In my code checking, the other archs can use self mmu_gather struct
since they code are excluded by HAVE_GENERIC_MMU_GATHER. In another word
if the code protected by HAVE_GENERIC_MMU_GATHER, it is safe for others
That is why tlb_flush_mmu/tlb_finish_mmu enabled both in mm/memory.c and
 other archs.

So, if the minimum change of tlb->start/end can be protected by
HAVE_GENERIC_MMU_GATHER, it is safe and harmless, am I right?

If so, the following patch should work on any condition.

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