linux-kernel - Re: [PATCH 06/14] mm: handle_pte_fault() use pte_offset_map_maywrite

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Message-ID: <b4bf605a-d31a-40ad-8cee-fe505e45dc64@bytedance.com>
Date: Wed, 21 Aug 2024 17:24:01 +0800
From: Qi Zheng <zhengqi.arch@...edance.com>
To: LEROY Christophe <christophe.leroy2@...soprasteria.com>
Cc: "david@...hat.com" <david@...hat.com>, "hughd@...gle.com"
 <hughd@...gle.com>, "willy@...radead.org" <willy@...radead.org>,
 "muchun.song@...ux.dev" <muchun.song@...ux.dev>,
 "vbabka@...nel.org" <vbabka@...nel.org>,
 "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
 "rppt@...nel.org" <rppt@...nel.org>,
 "vishal.moola@...il.com" <vishal.moola@...il.com>,
 "peterx@...hat.com" <peterx@...hat.com>,
 "ryan.roberts@....com" <ryan.roberts@....com>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "linux-mm@...ck.org" <linux-mm@...ck.org>,
 "linux-arm-kernel@...ts.infradead.org"
 <linux-arm-kernel@...ts.infradead.org>,
 "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH 06/14] mm: handle_pte_fault() use
 pte_offset_map_maywrite_nolock()



On 2024/8/21 17:17, LEROY Christophe wrote:
> 
> 
> Le 21/08/2024 à 10:18, Qi Zheng a écrit :
>> In handle_pte_fault(), we may modify the vmf->pte after acquiring the
>> vmf->ptl, so convert it to using pte_offset_map_maywrite_nolock(). But
>> since we already do the pte_same() check, so there is no need to get
>> pmdval to do pmd_same() check, just pass NULL to pmdvalp parameter.
>>
>> Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
>> ---
>>    mm/memory.c | 9 +++++++--
>>    1 file changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/mm/memory.c b/mm/memory.c
>> index 93c0c25433d02..d3378e98faf13 100644
>> --- a/mm/memory.c
>> +++ b/mm/memory.c
>> @@ -5504,9 +5504,14 @@ static vm_fault_t handle_pte_fault(struct vm_fault *vmf)
>>    		 * pmd by anon khugepaged, since that takes mmap_lock in write
>>    		 * mode; but shmem or file collapse to THP could still morph
>>    		 * it into a huge pmd: just retry later if so.
>> +		 *
>> +		 * Use the maywrite version to indicate that vmf->pte will be
>> +		 * modified, but since we will use pte_same() to detect the
>> +		 * change of the pte entry, there is no need to get pmdval.
>>    		 */
>> -		vmf->pte = pte_offset_map_nolock(vmf->vma->vm_mm, vmf->pmd,
>> -						 vmf->address, &vmf->ptl);
>> +		vmf->pte = pte_offset_map_maywrite_nolock(vmf->vma->vm_mm,
>> +							  vmf->pmd, vmf->address,
>> +							  NULL, &vmf->ptl);
> 
> This might be the demonstration that the function name is becoming too long.
> 
> Can you find shorter names ?

Maybe use abbreviations?

pte_offset_map_ro_nolock()
pte_offset_map_rw_nolock()

> 
>>    		if (unlikely(!vmf->pte))
>>    			return 0;
>>    		vmf->orig_pte = ptep_get_lockless(vmf->pte);