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SubjectRe: [PATCH] hugetlbfs: remove meaningless variable avoid_reserve
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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]);
>

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