Re: [PATCH 3/6] hugetlb: make hugetlb_fault_mutex_hash() take PAGE_SIZE index

[Oscar Salvador <osalvador@suse.de>]

On Thu, Apr 09, 2026 at 05:41:54PM -0600, Jane Chu wrote:
> hugetlb_fault_mutex_hash() is used to serialize faults and page cache
> operations on the same hugetlb file offset. The helper currently expects
> its index argument in hugetlb page granularity, so callers have to
> open-code conversions from the PAGE_SIZE-based indices commonly used
> in the rest of MM helpers.
> 
> Change hugetlb_fault_mutex_hash() to take a PAGE_SIZE-based index
> instead, and perform the hugetlb-granularity conversion inside the helper.
> Update all callers accordingly.
> 
> This makes the helper interface consistent with filemap_get_folio(),
> and linear_page_index(), while preserving the same lock selection for
> a given hugetlb file offset.
> 
> Signed-off-by: Jane Chu <jane.chu@oracle.com>
> ---
>  fs/hugetlbfs/inode.c | 19 ++++++++++---------
>  mm/hugetlb.c         | 28 +++++++++++++++++++---------
>  mm/memfd.c           | 11 ++++++-----
>  mm/userfaultfd.c     |  7 +++----
>  4 files changed, 38 insertions(+), 27 deletions(-)
> 
> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
> index cf79fb830377..e24e9bf54e14 100644
> --- a/fs/hugetlbfs/inode.c
> +++ b/fs/hugetlbfs/inode.c
> @@ -575,7 +575,7 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart,
>  	struct address_space *mapping = &inode->i_data;
>  	const pgoff_t end = lend >> PAGE_SHIFT;
>  	struct folio_batch fbatch;
> -	pgoff_t next, index;
> +	pgoff_t next, idx;
>  	int i, freed = 0;
>  	bool truncate_op = (lend == LLONG_MAX);
>  
> @@ -586,15 +586,15 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart,
>  			struct folio *folio = fbatch.folios[i];
>  			u32 hash = 0;
>  
> -			index = folio->index >> huge_page_order(h);
> -			hash = hugetlb_fault_mutex_hash(mapping, index);
> +			hash = hugetlb_fault_mutex_hash(mapping, folio->index);
>  			mutex_lock(&hugetlb_fault_mutex_table[hash]);
>  
>  			/*
>  			 * Remove folio that was part of folio_batch.
>  			 */
> +			idx = folio->index >> huge_page_order(h);
>  			remove_inode_single_folio(h, inode, mapping, folio,
> -						  index, truncate_op);
> +						  idx, truncate_op);

Since this is the only place we call remove_inode_single_folio(), and that we do not
the index (at least index >> huge_page_order()) directly in this function, would it not be
better to make remove_inode_single_folio do the conversion itself? 

Also, I am thinking out loud here but we do have a few places where we
go: idx = index >> huge_page_order() to convert it into hugepage units, but the casual
reader might be a bit puzzled about that.
So, would it be worth to have implement an inline helper with an accurate name
to do that? It might help whoever reads that?


-- 
Oscar Salvador
SUSE Labs