Re: [PATCH v7 2/4] mm/memory.c: Update local TLB if PTE entry exists

[maobibo <maobibo@loongson.cn>]

On 05/29/2020 03:23 AM, Andrew Morton wrote:
> On Wed, 27 May 2020 10:25:18 +0800 Bibo Mao <maobibo@loongson.cn> wrote:
> 
>> If two threads concurrently fault at the same page, the thread that
>> won the race updates the PTE and its local TLB. For now, the other
>> thread gives up, simply does nothing, and continues.
>>
>> It could happen that this second thread triggers another fault, whereby
>> it only updates its local TLB while handling the fault. Instead of
>> triggering another fault, let's directly update the local TLB of the
>> second thread. Function update_mmu_tlb is used here to update local
>> TLB on the second thread, and it is defined as empty on other arches.
>>
>> --- a/mm/memory.c
>> +++ b/mm/memory.c
>> @@ -2752,6 +2752,7 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf)
>>  		new_page = old_page;
>>  		page_copied = 1;
>>  	} else {
>> +		update_mmu_tlb(vma, vmf->address, vmf->pte);
>>  		mem_cgroup_cancel_charge(new_page, memcg, false);
>>  	}
>>  
> 
> When applying your patches on top of the -mm tree's changes, the above
> hunk didn't apply.  The entire `else' block was removed by
> https://ozlabs.org/~akpm/mmotm/broken-out/mm-memcontrol-convert-anon-and-file-thp-to-new-mem_cgroup_charge-api.patch
> 
> I assumed that dropping this hunk was appropriate.  Please check?
yes, that is appropriate. Sorry to bother you, originally I should format the
patch based on mm-tree.