linux-kernel - Re: [PATCH 03/16] mm/huge_memory: fix comment of __pud_trans_huge

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Date:   Sat, 25 Jun 2022 11:32:03 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     Matthew Wilcox <willy@...radead.org>
CC:     <akpm@...ux-foundation.org>, <shy828301@...il.com>,
        <zokeefe@...gle.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 03/16] mm/huge_memory: fix comment of
 __pud_trans_huge_lock

On 2022/6/25 2:56, Matthew Wilcox wrote:
> On Thu, Jun 23, 2022 at 01:06:14AM +0800, Miaohe Lin wrote:
>> __pud_trans_huge_lock returns page table lock pointer if a given pud maps
>> a thp instead of 'true' since introduced. Fix corresponding comments.
> 
> I think the comments here are rather wasted.  I think this comment
> should be moved to pud_trans_huge_lock() and turned into kernel-doc
> format.

Do you mean something like below? If so, __pmd_trans_huge_lock might need to do the
similar work?

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index ae3d8e2fd9e2..b73fe864de13 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -238,6 +238,12 @@ static inline spinlock_t *pmd_trans_huge_lock(pmd_t *pmd,
        else
                return NULL;
 }
+/**
+ * Returns true if a given pud maps a thp, false otherwise.
+ *
+ * Note that if it returns true, this routine returns without unlocking page
+ * table lock. So callers must unlock it.
+ */
 static inline spinlock_t *pud_trans_huge_lock(pud_t *pud,
                struct vm_area_struct *vma)
 {
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index eb2e4ecb76aa..ae4c2116be07 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2006,12 +2006,6 @@ spinlock_t *__pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma)
        return NULL;
 }

-/*
- * Returns true if a given pud maps a thp, false otherwise.
- *
- * Note that if it returns true, this routine returns without unlocking page
- * table lock. So callers must unlock it.
- */
 spinlock_t *__pud_trans_huge_lock(pud_t *pud, struct vm_area_struct *vma)
 {
        spinlock_t *ptl;

Thanks!
> 
>> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
>> ---
>>  mm/huge_memory.c | 6 +++---
>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>> index 83fb6c3442ff..a26580da8011 100644
>> --- a/mm/huge_memory.c
>> +++ b/mm/huge_memory.c
>> @@ -1903,10 +1903,10 @@ spinlock_t *__pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma)
>>  }
>>  
>>  /*
>> - * Returns true if a given pud maps a thp, false otherwise.
>> + * Returns page table lock pointer if a given pud maps a thp, NULL otherwise.
>>   *
>> - * Note that if it returns true, this routine returns without unlocking page
>> - * table lock. So callers must unlock it.
>> + * Note that if it returns page table lock pointe, this routine returns without
>> + * unlocking page table lock. So callers must unlock it.
>>   */
>>  spinlock_t *__pud_trans_huge_lock(pud_t *pud, struct vm_area_struct *vma)
>>  {
>> -- 
>> 2.23.0
>>
> 
> .
>