linux-kernel - Re: [PATCH] mm/rmap: vm_flags including VM

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Date:   Wed, 25 Oct 2023 11:04:46 +0800
From:   zhiguojiang <justinjiang@...o.com>
To:     David Hildenbrand <david@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Cc:     opensource.kernel@...o.com
Subject: Re: [PATCH] mm/rmap: vm_flags including VM_EXEC can exit timely



在 2023/10/25 9:17, zhiguojiang 写道:
>
>
> 在 2023/10/24 23:51, David Hildenbrand 写道:
>> On 24.10.23 16:49, Zhiguo Jiang wrote:
>>> When pra->vm_flags include VM_EXEC flag and folio is file detected in
>>> folio_referenced_one(), the folio referenced traversal process can be
>>> exited timely to reduce the detecting folio referenced time.
>>>
>>
>> Can you further elaborate what the logic behind that is?
>>
>> Why can we stop here if we're dealing with a pagecache folio in an 
>> executable VMA?
>>
> Functions call flow：folio_referenced() --> rmap_walk() --> 
> rmap_walk_ksm()/rmap_walk_anon()/rmap_walk_file() --> rwc->rmap_one() 
> --> folio_referenced_one(). And folio_referenced() is called by two 
> interfaces: folio_check_references() and shrink_active_list().
>
> 1. folio_check_references():
> When (referenced_ptes > 0 && (vm_flags & VM_EXEC) && 
> folio_is_file_lru(folio)) is detected in folio_check_references(), 
> FOLIOREF_ACTIVATE will be returned and the folio will be added to the 
> active file lru. So when VM_EXEC is detected in 
> folio_referenced_one(), we can stop continuing to detect the reference 
> relationship between this folio and other vmas, and exit directly to 
> avoid unnecessary traversal.
>
> 2. shrink_active_list():
> The shrink_active_list() is the same as the folio_check_references().
>
>>> Signed-off-by: Zhiguo Jiang <justinjiang@...o.com>
>>> ---
>>>   mm/rmap.c | 2 ++
>>>   1 file changed, 2 insertions(+)
>>>   mode change 100644 => 100755 mm/rmap.c
>>>
>>> diff --git a/mm/rmap.c b/mm/rmap.c
>>> index 7a27a2b41802..932f3b7e8521
>>> --- a/mm/rmap.c
>>> +++ b/mm/rmap.c
>>> @@ -884,6 +884,8 @@ static bool folio_referenced_one(struct folio 
>>> *folio,
>>>       if (referenced) {
>>>           pra->referenced++;
>>>           pra->vm_flags |= vma->vm_flags & ~VM_LOCKED;
>>> +        if ((pra->vm_flags | VM_EXEC) && folio_is_file_lru(folio))
>>> +            return false;
>>>       }
>>>         if (!pra->mapcount)
Sorry, Patch mistake in writing, patch should be:
+        if ((pra->vm_flags & VM_EXEC) && folio_is_file_lru(folio))
+            return false;
>>
>