linux-kernel - Re: [RFC PATCH 2/4] mm: Change the interface for __tlb_remove

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Message-ID: <87mvn71rwc.fsf@skywalker.in.ibm.com>
Date:	Mon, 30 May 2016 21:04:27 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Hillf Danton <hillf.zj@...baba-inc.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>, linux-mm@...ck.org
Subject: Re: [RFC PATCH 2/4] mm: Change the interface for __tlb_remove_page

Hillf Danton <hillf.zj@...baba-inc.com> writes:

>> diff --git a/mm/memory.c b/mm/memory.c
>> index 15322b73636b..a01db5bc756b 100644
>> --- a/mm/memory.c
>> +++ b/mm/memory.c
>> @@ -292,23 +292,24 @@ void tlb_finish_mmu(struct mmu_gather *tlb, unsigned long start, unsigned long e
>>   *	handling the additional races in SMP caused by other CPUs caching valid
>>   *	mappings in their TLBs. Returns the number of free page slots left.
>>   *	When out of page slots we must call tlb_flush_mmu().
>> + *returns true if the caller should flush.
>>   */
>> -int __tlb_remove_page(struct mmu_gather *tlb, struct page *page)
>> +bool __tlb_remove_page(struct mmu_gather *tlb, struct page *page)
>>  {
>>  	struct mmu_gather_batch *batch;
>> 
>>  	VM_BUG_ON(!tlb->end);
>> 
>>  	batch = tlb->active;
>> -	batch->pages[batch->nr++] = page;
>>  	if (batch->nr == batch->max) {
>>  		if (!tlb_next_batch(tlb))
>> -			return 0;
>> +			return true;
>>  		batch = tlb->active;
>>  	}
>>  	VM_BUG_ON_PAGE(batch->nr > batch->max, page);
>
> Still needed?

yes, we need to make sure the batch we picked doesn't have a wrong
batch->nr value.

>> 
>> -	return batch->max - batch->nr;
>> +	batch->pages[batch->nr++] = page;
>> +	return false;
>>  }
>> 
>>  #endif /* HAVE_GENERIC_MMU_GATHER */
>> @@ -1109,6 +1110,7 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
>>  	pte_t *start_pte;
>>  	pte_t *pte;
>>  	swp_entry_t entry;
>> +	struct page *pending_page = NULL;
>> 
>>  again:
>>  	init_rss_vec(rss);
>> @@ -1160,8 +1162,9 @@ again:
>>  			page_remove_rmap(page, false);
>>  			if (unlikely(page_mapcount(page) < 0))
>>  				print_bad_pte(vma, addr, ptent, page);
>> -			if (unlikely(!__tlb_remove_page(tlb, page))) {
>> +			if (unlikely(__tlb_remove_page(tlb, page))) {
>>  				force_flush = 1;
>> +				pending_page = page;
>>  				addr += PAGE_SIZE;
>>  				break;
>>  			}
>> @@ -1202,7 +1205,12 @@ again:
>>  	if (force_flush) {
>>  		force_flush = 0;
>>  		tlb_flush_mmu_free(tlb);
>> -
>> +		if (pending_page) {
>> +			/* remove the page with new size */
>> +			__tlb_adjust_range(tlb, tlb->addr);
>
> Would you please specify why tlb->addr is used here?
>

That is needed because tlb_flush_mmu_tlbonly() does a __tlb_reset_range().


>> +			__tlb_remove_page(tlb, pending_page);
>> +			pending_page = NULL;
>> +		}
>>  		if (addr != end)
>>  			goto again;
>>  	}
>> --
>> 2.7.4

-aneesh