On Tue, Oct 03, 2023 at 12:44:45AM -0700, Vivek Kasireddy wrote:
> +/**
> + * pin_user_pages_fd() - pin user pages associated with a file
> + * @fd: the fd whose pages are to be pinned
> + * @start: starting file offset
> + * @nr_pages: number of pages from start to pin
> + * @gup_flags: flags modifying pin behaviour
> + * @pages: array that receives pointers to the pages pinned.
> + * Should be at least nr_pages long.
> + *
> + * Attempt to pin (and migrate) pages associated with a file belonging to
> + * either shmem or hugetlbfs. An error is returned if pages associated with
> + * hugetlbfs files are not present in the page cache. However, shmem pages
> + * are swapped in or allocated if they are not present in the page cache.
> + *
> + * Returns number of pages pinned. This would be equal to the number of
> + * pages requested.
> + * If nr_pages is 0 or negative, returns 0. If no pages were pinned, returns
> + * -errno.
> + */
> +long pin_user_pages_fd(int fd, pgoff_t start, unsigned long nr_pages,
> + unsigned int gup_flags, struct page **pages)
> +{
> + struct page *page;
> + struct file *filep;
> + unsigned int flags, i;
> + long ret;
> +
> + if (nr_pages <= 0)
> + return 0;
> + if (!is_valid_gup_args(pages, NULL, &gup_flags, FOLL_PIN))
> + return 0;
> +
> + if (start < 0)
> + return -EINVAL;
> +
> + filep = fget(fd);
> + if (!filep)
> + return -EINVAL;
I think the caller should pass in the file *
In some cases we will need to hold a reference on it for a long time.
> + if (!shmem_file(filep) && !is_file_hugepages(filep))
> + return -EINVAL;
> +
> + flags = memalloc_pin_save();
> + do {
> + for (i = 0; i < nr_pages; i++) {
> + if (shmem_mapping(filep->f_mapping)) {
> + page = shmem_read_mapping_page(filep->f_mapping,
> + start + i);
> + if (IS_ERR(page)) {
> + ret = PTR_ERR(page);
> + goto err;
> + }
> + } else {
> + page = find_get_page_flags(filep->f_mapping,
> + start + i,
> + FGP_ACCESSED);
> + if (!page) {
> + ret = -EINVAL;
> + goto err;
> + }
I don't know these APIs at all, but I admit to being surprised we need
the special case for shmem ?
> + ret = try_grab_page(page, FOLL_PIN);
> + if (unlikely(ret))
> + goto err;
> +
> + pages[i] = page;
> + put_page(pages[i]);
> + }
> +
> + ret = check_and_migrate_movable_pages(nr_pages, pages);
> + } while (ret == -EAGAIN);
It seems OK, but I do wish it was faster :) Maybe for another day.
Jason
