linux-kernel - Re: [PATCH 04/16] mm/huge_memory: use helper touch_pud in huge_pud_set

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Date:   Thu, 23 Jun 2022 20:08:47 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     Muchun Song <songmuchun@...edance.com>
CC:     <akpm@...ux-foundation.org>, <shy828301@...il.com>,
        <willy@...radead.org>, <zokeefe@...gle.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 04/16] mm/huge_memory: use helper touch_pud in
 huge_pud_set_accessed

On 2022/6/23 14:42, Muchun Song wrote:
> On Thu, Jun 23, 2022 at 01:06:15AM +0800, Miaohe Lin wrote:
>> Use helper touch_pud to set pud accessed to simplify the code and improve
>> the readability. No functional change intended.
>>
>> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
>> ---
>>  mm/huge_memory.c | 14 ++++----------
>>  1 file changed, 4 insertions(+), 10 deletions(-)
>>
>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>> index a26580da8011..a0c0e4bf9c1e 100644
>> --- a/mm/huge_memory.c
>> +++ b/mm/huge_memory.c
>> @@ -1281,21 +1281,15 @@ int copy_huge_pud(struct mm_struct *dst_mm, struct mm_struct *src_mm,
>>  
>>  void huge_pud_set_accessed(struct vm_fault *vmf, pud_t orig_pud)
>>  {
>> -	pud_t entry;
>> -	unsigned long haddr;
>> -	bool write = vmf->flags & FAULT_FLAG_WRITE;
>> +	int flags = 0;
>>  
>>  	vmf->ptl = pud_lock(vmf->vma->vm_mm, vmf->pud);
>>  	if (unlikely(!pud_same(*vmf->pud, orig_pud)))
>>  		goto unlock;
>>  
>> -	entry = pud_mkyoung(orig_pud);
>> -	if (write)
>> -		entry = pud_mkdirty(entry);
>> -	haddr = vmf->address & HPAGE_PUD_MASK;
>> -	if (pudp_set_access_flags(vmf->vma, haddr, vmf->pud, entry, write))
>> -		update_mmu_cache_pud(vmf->vma, vmf->address, vmf->pud);
>> -
>> +	if (vmf->flags & FAULT_FLAG_WRITE)
>> +		flags = FOLL_WRITE;
> 
> FOLL_* flags are used for follow_page(). But huge_pud_set_accessed() is used in mm fault
> path. It is a little weird to me to use FOLL_WRITE here. I suggest replace the last
> parameter of touch_pud() to "bool writable", then passing "vmf->flags & FAULT_FLAG_WRITE"
> to it instead of converting from FAULT_FLAG* flag to FOLL* flag.

Sounds good. Thanks!

> 
> Thanks.
> 
>> +	touch_pud(vmf->vma, vmf->address, vmf->pud, flags);
>>  unlock:
>>  	spin_unlock(vmf->ptl);
>>  }
>> -- 
>> 2.23.0
>>
>>
> .
>