> +static struct page *alloc_file_page(struct file *file, pgoff_t idx)
alloc_file_pages seems like a weird name for something that assumes
it is called either on a hugetlbfs or shmemfs file (without any
asserts that this is true). gup.c also seems like a very odd place
for such a helper.
> + * Attempt to pin pages associated with a file that belongs to either shmem
> + * or hugetlb.
Why do we need a special case for hugetlb or shmemfs?
> + if (!file)
> + return -EINVAL;
> +
> + if (!shmem_file(file) && !is_file_hugepages(file))
> + return -EINVAL;
Indentation is messed up here.
> + for (i = 0; i < nr_pages; i++) {
> + /*
> + * In most cases, we should be able to find the page
> + * in the page cache. If we cannot find it, we try to
> + * allocate one and add it to the page cache.
> + */
> +retry:
> + folio = __filemap_get_folio(file->f_mapping,
> + start + i,
> + FGP_ACCESSED, 0);
__filemap_get_folio is a very inefficient way to find a
contiguous range of folios, I'd suggest to look into something that
batches instead.
> + page = IS_ERR(folio) ? NULL: &folio->page;
> + if (!page) {
> + page = alloc_file_page(file, start + i);
> + if (IS_ERR(page)) {
> + ret = PTR_ERR(page);
> + if (ret == -EEXIST)
> + goto retry;
> + goto err;
> + }
This mix of folios and pages is odd. Especially as hugetlbfs by
definitions uses large folios.
