[PATCH] hugetlbfs: remove meaningless variable avoid_reserve

[PATCH] hugetlbfs: remove meaningless variable avoid_reserve

[Miaohe Lin]

The variable avoid_reserve is meaningless because we never changed its
value and just passed it to alloc_huge_page(). So remove it to make code
more clear that in hugetlbfs_fallocate, we never avoid reserve when alloc
hugepage yet.

Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
---
 fs/hugetlbfs/inode.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 88751e35e69d..23ad6ed8b75f 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -680,7 +680,6 @@ static long hugetlbfs_fallocate(struct file *file, int mode, loff_t offset,
 		 */
 		struct page *page;
 		unsigned long addr;
-		int avoid_reserve = 0;
 
 		cond_resched();
 
@@ -717,7 +716,7 @@ static long hugetlbfs_fallocate(struct file *file, int mode, loff_t offset,
 		}
 
 		/* Allocate page and add to page cache */
-		page = alloc_huge_page(&pseudo_vma, addr, avoid_reserve);
+		page = alloc_huge_page(&pseudo_vma, addr, 0);
 		hugetlb_drop_vma_policy(&pseudo_vma);
 		if (IS_ERR(page)) {
 			mutex_unlock(&hugetlb_fault_mutex_table[hash]);
-- 
2.19.1

Re: [PATCH] hugetlbfs: remove meaningless variable avoid_reserve

[Souptick Joarder]

On Sat, Jan 16, 2021 at 2:57 PM Miaohe Lin <linmiaohe@huawei.com> wrote:
>
> The variable avoid_reserve is meaningless because we never changed its
> value and just passed it to alloc_huge_page(). So remove it to make code
> more clear that in hugetlbfs_fallocate, we never avoid reserve when alloc
> hugepage yet.
>
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>

Acked-by: Souptick Joarder <jrdr.linux@gmail.com>

> ---
>  fs/hugetlbfs/inode.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
> index 88751e35e69d..23ad6ed8b75f 100644
> --- a/fs/hugetlbfs/inode.c
> +++ b/fs/hugetlbfs/inode.c
> @@ -680,7 +680,6 @@ static long hugetlbfs_fallocate(struct file *file, int mode, loff_t offset,
>                  */
>                 struct page *page;
>                 unsigned long addr;
> -               int avoid_reserve = 0;
>
>                 cond_resched();
>
> @@ -717,7 +716,7 @@ static long hugetlbfs_fallocate(struct file *file, int mode, loff_t offset,
>                 }
>
>                 /* Allocate page and add to page cache */
> -               page = alloc_huge_page(&pseudo_vma, addr, avoid_reserve);
> +               page = alloc_huge_page(&pseudo_vma, addr, 0);
>                 hugetlb_drop_vma_policy(&pseudo_vma);
>                 if (IS_ERR(page)) {
>                         mutex_unlock(&hugetlb_fault_mutex_table[hash]);
> --
> 2.19.1
>
>

Re: [PATCH] hugetlbfs: remove meaningless variable avoid_reserve

[David Hildenbrand]

On 16.01.21 10:26, Miaohe Lin wrote:
> The variable avoid_reserve is meaningless because we never changed its
> value and just passed it to alloc_huge_page(). So remove it to make code
> more clear that in hugetlbfs_fallocate, we never avoid reserve when alloc
> hugepage yet.
> 
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
> ---
>  fs/hugetlbfs/inode.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
> index 88751e35e69d..23ad6ed8b75f 100644
> --- a/fs/hugetlbfs/inode.c
> +++ b/fs/hugetlbfs/inode.c
> @@ -680,7 +680,6 @@ static long hugetlbfs_fallocate(struct file *file, int mode, loff_t offset,
>  		 */
>  		struct page *page;
>  		unsigned long addr;
> -		int avoid_reserve = 0;
>  
>  		cond_resched();
>  
> @@ -717,7 +716,7 @@ static long hugetlbfs_fallocate(struct file *file, int mode, loff_t offset,
>  		}
>  
>  		/* Allocate page and add to page cache */
> -		page = alloc_huge_page(&pseudo_vma, addr, avoid_reserve);
> +		page = alloc_huge_page(&pseudo_vma, addr, 0);
>  		hugetlb_drop_vma_policy(&pseudo_vma);
>  		if (IS_ERR(page)) {
>  			mutex_unlock(&hugetlb_fault_mutex_table[hash]);
> 

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 
Thanks,

David / dhildenb

Re: [PATCH] hugetlbfs: remove meaningless variable avoid_reserve

[Mike Kravetz]

Please CC Andrew on hugetlb patches as they need to go through his tree.

On 1/16/21 1:26 AM, Miaohe Lin wrote:
> The variable avoid_reserve is meaningless because we never changed its
> value and just passed it to alloc_huge_page(). So remove it to make code
> more clear that in hugetlbfs_fallocate, we never avoid reserve when alloc
> hugepage yet.

One might argue that using a named variable makes the call to alloc_huge_page
more clear.  I do not disagree with the change,  However, there are some
subtle reasons why alloc_huge_page is called with 'avoid_reserve = 0' from
fallocate.  Therefore, I would prefer that a comment be added above the call
in addition to this change.  See below.

> 
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
> ---
>  fs/hugetlbfs/inode.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
> index 88751e35e69d..23ad6ed8b75f 100644
> --- a/fs/hugetlbfs/inode.c
> +++ b/fs/hugetlbfs/inode.c
> @@ -680,7 +680,6 @@ static long hugetlbfs_fallocate(struct file *file, int mode, loff_t offset,
>  		 */
>  		struct page *page;
>  		unsigned long addr;
> -		int avoid_reserve = 0;
>  
>  		cond_resched();
>  
> @@ -717,7 +716,7 @@ static long hugetlbfs_fallocate(struct file *file, int mode, loff_t offset,
>  		}
>  
>  		/* Allocate page and add to page cache */

Perhaps, change comment to read:

		/*
		 * Allocate page without setting the avoid_reserve argument.
		 * There certainly are no reserves associated with the
		 * pseudo_vma.  However, there could be shared mappings with
		 * reserves for the file at the inode level.  If we fallocate
		 * pages in these areas, we need to consume the reserves
		 * to keep reservation accounting consistent.
		 */

-- 
Mike Kravetz

> -		page = alloc_huge_page(&pseudo_vma, addr, avoid_reserve);
> +		page = alloc_huge_page(&pseudo_vma, addr, 0);
>  		hugetlb_drop_vma_policy(&pseudo_vma);
>  		if (IS_ERR(page)) {
>  			mutex_unlock(&hugetlb_fault_mutex_table[hash]);
> 

Re: [PATCH] hugetlbfs: remove meaningless variable avoid_reserve

[Miaohe Lin]

Hi:
On 2021/1/20 2:41, Mike Kravetz wrote:
> Please CC Andrew on hugetlb patches as they need to go through his tree.
> 
> On 1/16/21 1:26 AM, Miaohe Lin wrote:
>> The variable avoid_reserve is meaningless because we never changed its
>> value and just passed it to alloc_huge_page(). So remove it to make code
>> more clear that in hugetlbfs_fallocate, we never avoid reserve when alloc
>> hugepage yet.
> 
> One might argue that using a named variable makes the call to alloc_huge_page
> more clear.  I do not disagree with the change,  However, there are some
> subtle reasons why alloc_huge_page is called with 'avoid_reserve = 0' from
> fallocate.  Therefore, I would prefer that a comment be added above the call
> in addition to this change.  See below.
> 
>>
>> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
>> ---
>>  fs/hugetlbfs/inode.c | 3 +--
>>  1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
>> index 88751e35e69d..23ad6ed8b75f 100644
>> --- a/fs/hugetlbfs/inode.c
>> +++ b/fs/hugetlbfs/inode.c
>> @@ -680,7 +680,6 @@ static long hugetlbfs_fallocate(struct file *file, int mode, loff_t offset,
>>  		 */
>>  		struct page *page;
>>  		unsigned long addr;
>> -		int avoid_reserve = 0;
>>  
>>  		cond_resched();
>>  
>> @@ -717,7 +716,7 @@ static long hugetlbfs_fallocate(struct file *file, int mode, loff_t offset,
>>  		}
>>  
>>  		/* Allocate page and add to page cache */
> 
> Perhaps, change comment to read:
> 
> 		/*
> 		 * Allocate page without setting the avoid_reserve argument.
> 		 * There certainly are no reserves associated with the
> 		 * pseudo_vma.  However, there could be shared mappings with
> 		 * reserves for the file at the inode level.  If we fallocate
> 		 * pages in these areas, we need to consume the reserves
> 		 * to keep reservation accounting consistent.
> 		 */
> 

Many thanks for detailed and excellent comment. Will do it in v2.
Thanks again.