linux-kernel - Re: [PATCH] hugetlbfs: remove meaningless variable avoid

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Message-ID: <52159266-f3bf-1043-9f63-f6147355f043@huawei.com>
Date:   Wed, 20 Jan 2021 10:10:08 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>
CC:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] hugetlbfs: remove meaningless variable avoid_reserve

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@...wei.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.