linux-kernel - Re: [PATCH v2 5/5] mm: Add update_mmu_tlb

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Message-ID: <41acfd35-69b4-41bc-a45b-4426d5110077@antgroup.com>
Date: Sat, 11 May 2024 00:36:35 +0800
From: "Bang Li" <libang.li@...group.com>
To: Ryan Roberts <ryan.roberts@....com>, akpm@...ux-foundation.org,
 chenhuacai@...nel.org, tsbogend@...ha.franken.de, paul.walmsley@...ive.com,
 palmer@...belt.com, chris@...kel.net, jcmvbkbc@...il.com
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 loongarch@...ts.linux.dev, linux-riscv@...ts.infradead.org,
 david@...hat.com, ioworker0@...il.com, libang.linux@...il.com,
 baolin.wang@...ux.alibaba.com
Subject: Re: [PATCH v2 5/5] mm: Add update_mmu_tlb_range()

Hi Ryan,

Thanks for you review!

On 2024/5/10 17:05, Ryan Roberts wrote:
> On 06/05/2024 16:51, Bang Li wrote:
>> After the commit 19eaf44954df ("mm: thp: support allocation of anonymous
>> multi-size THP"), it may need to batch update tlb of an address range
>> through the update_mmu_tlb function. We can simplify this operation by
>> adding the update_mmu_tlb_range function, which may also reduce the
>> execution of some unnecessary code in some architectures.
>>
>> Signed-off-by: Bang Li <libang.li@...group.com>
>> ---
>>   include/linux/pgtable.h | 8 ++++++++
>>   mm/memory.c             | 4 +---
>>   2 files changed, 9 insertions(+), 3 deletions(-)
>>
>> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
>> index 18019f037bae..869bfe6054f1 100644
>> --- a/include/linux/pgtable.h
>> +++ b/include/linux/pgtable.h
>> @@ -737,6 +737,14 @@ static inline void update_mmu_tlb(struct vm_area_struct *vma,
>>   #define __HAVE_ARCH_UPDATE_MMU_TLB
>>   #endif
> 
> Given you are implementing update_mmu_tlb_range() in all the arches that
> currently override update_mmu_tlb() I wonder if it would be cleaner to remove
> update_mmu_tlb() from all those arches, and define generically, removing the
> ability for arches to override it:
> 
> static inline void update_mmu_tlb(struct vm_area_struct *vma,
> 				unsigned long address, pte_t *ptep)
> {
> 	update_mmu_tlb_range(vma, address, ptep, 1);
> }

Agreed! Thank you for your suggestion, I will modify it in the next version.

> 
>>   
>> +#ifndef __HAVE_ARCH_UPDATE_MMU_TLB_RANGE
>> +static inline void update_mmu_tlb_range(struct vm_area_struct *vma,
>> +				unsigned long address, pte_t *ptep, unsigned int nr)
>> +{
>> +}
>> +#define __HAVE_ARCH_UPDATE_MMU_TLB_RANGE
>> +#endif
> 
> Then you could use the modern override scheme as Lance suggested and you won't
> have any confusion with __HAVE_ARCH_UPDATE_MMU_TLB because it won't exist anymore.

Yes, use update_mmu_tlb_range to implement update_mmu_tlb, we only need 
to define the update_mmu_tlb_range macro.

> 
>> +
>>   /*
>>    * Some architectures may be able to avoid expensive synchronization
>>    * primitives when modifications are made to PTE's which are already
>> diff --git a/mm/memory.c b/mm/memory.c
>> index eea6e4984eae..2d53e29cf76e 100644
>> --- a/mm/memory.c
>> +++ b/mm/memory.c
>> @@ -4421,7 +4421,6 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
>>   	vm_fault_t ret = 0;
>>   	int nr_pages = 1;
>>   	pte_t entry;
>> -	int i;
>>   
>>   	/* File mapping without ->vm_ops ? */
>>   	if (vma->vm_flags & VM_SHARED)
>> @@ -4491,8 +4490,7 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
>>   		update_mmu_tlb(vma, addr, vmf->pte);
>>   		goto release;
>>   	} else if (nr_pages > 1 && !pte_range_none(vmf->pte, nr_pages)) {
>> -		for (i = 0; i < nr_pages; i++)
>> -			update_mmu_tlb(vma, addr + PAGE_SIZE * i, vmf->pte + i);
>> +		update_mmu_tlb_range(vma, addr, vmf->pte, nr_pages);
> 
> I certainly agree that this will be a useful helper to have. I expect there will
> be more users in future.

Thank you for your affirmation. Baolin’s "add mTHP support for anonymous 
shmem" series[1] can also use this function to simplify the code.

[1] 
https://lore.kernel.org/linux-mm/cover.1714978902.git.baolin.wang@linux.alibaba.com/

Thanks,
Bang

> 
>>   		goto release;
>>   	}
>>