[PATCH v20 02/32] splice: Clean up direct_splice_read() a bit

From: David Howells
Date: Fri May 19 2023 - 03:42:27 EST


Do a couple of cleanups to direct_splice_read():

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

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

Suggested-by: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
cc: Jens Axboe <axboe@xxxxxxxxx>
cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
cc: David Hildenbrand <david@xxxxxxxxxx>
cc: John Hubbard <jhubbard@xxxxxxxxxx>
cc: linux-mm@xxxxxxxxx
cc: linux-block@xxxxxxxxxxxxxxx
cc: linux-fsdevel@xxxxxxxxxxxxxxx
---
fs/splice.c | 19 +++++++------------
1 file changed, 7 insertions(+), 12 deletions(-)

diff --git a/fs/splice.c b/fs/splice.c
index 3e06611d19ae..4db3eee49423 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -312,7 +312,7 @@ ssize_t direct_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 */
@@ -326,7 +326,7 @@ ssize_t direct_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);
@@ -349,11 +349,8 @@ ssize_t direct_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) {
@@ -366,14 +363,12 @@ ssize_t direct_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);