On Wed, Aug 19, 2020 at 04:05:50PM +0100, Matthew Wilcox (Oracle) wrote:
> use the XArray directly instead of using the pagevec abstraction.
> The code is simpler and more efficient.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> ---
> mm/shmem.c | 61 +++++++++++++++++++++---------------------------------
> 1 file changed, 24 insertions(+), 37 deletions(-)
>
> diff --git a/mm/shmem.c b/mm/shmem.c
> index a7bbc4ed9677..0f9f149f4b5e 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -2659,53 +2659,40 @@ static ssize_t shmem_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
> }
>
> /*
> - * llseek SEEK_DATA or SEEK_HOLE through the page cache.
> + * llseek SEEK_DATA or SEEK_HOLE through the page cache. We don't need
> + * to get a reference on the page because this interface is racy anyway.
> + * The page we find will have had the state at some point.
For my non-native ear "will have had" is too complex ;-)
> */
> static pgoff_t shmem_seek_hole_data(struct address_space *mapping,
> pgoff_t index, pgoff_t end, int whence)
> {
> + XA_STATE(xas, &mapping->i_pages, index);
> struct page *page;
> - struct pagevec pvec;
> - pgoff_t indices[PAGEVEC_SIZE];
> - bool done = false;
> - int i;
>
> - pagevec_init(&pvec);
> - pvec.nr = 1; /* start small: we may be there already */
> - while (!done) {
> - pvec.nr = find_get_entries(mapping, index,
> - pvec.nr, pvec.pages, indices);
> - if (!pvec.nr) {
> - if (whence == SEEK_DATA)
> - index = end;
> - break;
> + rcu_read_lock();
> + if (whence == SEEK_DATA) {
> + for (;;) {
> + page = xas_find(&xas, end);
> + if (xas_retry(&xas, page))
> + continue;
> + if (!page || xa_is_value(page) || PageUptodate(page))
> + break;
> }
> - for (i = 0; i < pvec.nr; i++, index++) {
> - if (index < indices[i]) {
> - if (whence == SEEK_HOLE) {
> - done = true;
> - break;
> - }
> - index = indices[i];
> - }
> - page = pvec.pages[i];
> - if (page && !xa_is_value(page)) {
> - if (!PageUptodate(page))
> - page = NULL;
> - }
> - if (index >= end ||
> - (page && whence == SEEK_DATA) ||
> - (!page && whence == SEEK_HOLE)) {
> - done = true;
> + } else /* SEEK_HOLE */ {
> + for (;;) {
> + page = xas_next(&xas);
> + if (xas_retry(&xas, page))
> + continue;
> + if (!xa_is_value(page) &&
> + (!page || !PageUptodate(page)))
> + break;
> + if (xas.xa_index >= end)
> break;
> - }
> }
> - pagevec_remove_exceptionals(&pvec);
> - pagevec_release(&pvec);
> - pvec.nr = PAGEVEC_SIZE;
> - cond_resched();
> }
> - return index;
> + rcu_read_unlock();
> +
> + return xas.xa_index;
> }
>
> static loff_t shmem_file_llseek(struct file *file, loff_t offset, int whence)
> --
> 2.28.0
>
>
--
Sincerely yours,
Mike.
