Re: [PATCH v2 04/11] hugetlbfs,filemap: replace hugetlbfs_read_iter() with generic_file_read_iter()

[Matthew Wilcox <willy@infradead.org>]

On Wed, Jun 17, 2026 at 11:25:25AM -0600, Jane Chu wrote:
> +++ b/mm/filemap.c
> @@ -2672,20 +2672,30 @@ static int filemap_get_pages(struct kiocb *iocb, size_t count,
>  {
>  	struct file *filp = iocb->ki_filp;
>  	struct address_space *mapping = filp->f_mapping;
> +	bool is_hugetlbfs = is_file_hugepages(filp);
>  	pgoff_t index = iocb->ki_pos >> PAGE_SHIFT;
>  	pgoff_t last_index;
>  	struct folio *folio;
>  	unsigned int flags;
> +	size_t min_folio_bytes;
>  	int err = 0;
>  
>  	/* "last_index" is the index of the folio beyond the end of the read */
> -	last_index = round_up(iocb->ki_pos + count,
> -			mapping_min_folio_nrbytes(mapping)) >> PAGE_SHIFT;
> +	if (is_hugetlbfs)
> +		min_folio_bytes = huge_page_size(hstate_file(filp));
> +	else
> +		min_folio_bytes = mapping_min_folio_nrbytes(mapping);
> +	last_index = round_up(iocb->ki_pos + count, min_folio_bytes) >> PAGE_SHIFT;

I don't love this.  Is there a way we can get mapping_min_folio_nrbytes()
to give us the right number for hugetlbfs?  I don't see why it wouldn't
be possible ...

>  	filemap_get_read_batch(mapping, index, last_index - 1, fbatch);
> +
> +	if (is_hugetlbfs)
> +		goto done;

We don't actually need this, do we?  For hugetlbfs, I don't think we
can get 0 folios in the batch, and then we won't find a folio with
readahead set, and they're always uptodate ... so we're just skipping a
few tests with this?