splice: Clean up copy_splice_read() a bit

Do a couple of cleanups to copy_splice_read():

 (1) Cast to struct page **, not void *.

 (2) Simplify the calculation of the number of pages to keep/reclaim in
     copy_splice_read().

Suggested-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Christian Brauner <brauner@kernel.org>
cc: Jens Axboe <axboe@kernel.dk>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: David Hildenbrand <david@redhat.com>
cc: John Hubbard <jhubbard@nvidia.com>
cc: linux-mm@kvack.org
cc: linux-block@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
Link: https://lore.kernel.org/r/20230522135018.2742245-5-dhowells@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/splice.c b/fs/splice.c
index 2478e06..f9a9be7 100644 (file)
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -311,7 +311,7 @@ ssize_t copy_splice_read(struct file *in, loff_t *ppos,
        struct kiocb kiocb;
        struct page **pages;
        ssize_t ret;
-       size_t used, npages, chunk, remain, reclaim;
+       size_t used, npages, chunk, remain, keep = 0;
        int i;
 
        /* Work out how much data we can actually add into the pipe */
@@ -325,7 +325,7 @@ ssize_t copy_splice_read(struct file *in, loff_t *ppos,
        if (!bv)
                return -ENOMEM;
 
-       pages = (void *)(bv + npages);
+       pages = (struct page **)(bv + npages);
        npages = alloc_pages_bulk_array(GFP_USER, npages, pages);
        if (!npages) {
                kfree(bv);
@@ -348,11 +348,8 @@ ssize_t copy_splice_read(struct file *in, loff_t *ppos,
        kiocb.ki_pos = *ppos;
        ret = call_read_iter(in, &kiocb, &to);
 
-       reclaim = npages * PAGE_SIZE;
-       remain = 0;
        if (ret > 0) {
-               reclaim -= ret;
-               remain = ret;
+               keep = DIV_ROUND_UP(ret, PAGE_SIZE);
                *ppos = kiocb.ki_pos;
                file_accessed(in);
        } else if (ret < 0) {
@@ -365,14 +362,12 @@ ssize_t copy_splice_read(struct file *in, loff_t *ppos,
        }
 
        /* Free any pages that didn't get touched at all. */
-       reclaim /= PAGE_SIZE;
-       if (reclaim) {
-               npages -= reclaim;
-               release_pages(pages + npages, reclaim);
-       }
+       if (keep < npages)
+               release_pages(pages + keep, npages - keep);
 
        /* Push the remaining pages into the pipe. */
-       for (i = 0; i < npages; i++) {
+       remain = ret;
+       for (i = 0; i < keep; i++) {
                struct pipe_buffer *buf = pipe_head_buf(pipe);
 
                chunk = min_t(size_t, remain, PAGE_SIZE);