[RFC PATCH 3/4] splice: Remove some now-unused bits

From: David Howells
Date: Thu Jun 29 2023 - 11:56:16 EST

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Remove some code that's no longer used as the ->confirm() op is no longer
used and pages spliced in from the pagecache and process VM are now
pre-stolen or copied.

Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
cc: Dave Chinner <david@xxxxxxxxxxxxx>
cc: Christoph Hellwig <hch@xxxxxx>
cc: Jens Axboe <axboe@xxxxxxxxx>
cc: linux-fsdevel@xxxxxxxxxxxxxxx
---
fs/fuse/dev.c | 37 ---------
fs/pipe.c | 12 ---
fs/splice.c | 155 +-------------------------------------
include/linux/pipe_fs_i.h | 14 ----
include/linux/splice.h | 1 -
mm/filemap.c | 2 +-
6 files changed, 3 insertions(+), 218 deletions(-)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 1a8f82f478cb..9718dce0f0d9 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -700,10 +700,6 @@ static int fuse_copy_fill(struct fuse_copy_state *cs)
struct pipe_buffer *buf = cs->pipebufs;

if (!cs->write) {
- err = pipe_buf_confirm(cs->pipe, buf);
- if (err)
- return err;
-
BUG_ON(!cs->nr_segs);
cs->currbuf = buf;
cs->pg = buf->page;
@@ -766,26 +762,6 @@ static int fuse_copy_do(struct fuse_copy_state *cs, void **val, unsigned *size)
return ncpy;
}

-static int fuse_check_folio(struct folio *folio)
-{
- if (folio_mapped(folio) ||
- folio->mapping != NULL ||
- (folio->flags & PAGE_FLAGS_CHECK_AT_PREP &
- ~(1 << PG_locked |
- 1 << PG_referenced |
- 1 << PG_uptodate |
- 1 << PG_lru |
- 1 << PG_active |
- 1 << PG_workingset |
- 1 << PG_reclaim |
- 1 << PG_waiters |
- LRU_GEN_MASK | LRU_REFS_MASK))) {
- dump_page(&folio->page, "fuse: trying to steal weird page");
- return 1;
- }
- return 0;
-}
-
static int fuse_try_move_page(struct fuse_copy_state *cs, struct page **pagep)
{
int err;
@@ -800,10 +776,6 @@ static int fuse_try_move_page(struct fuse_copy_state *cs, struct page **pagep)

fuse_copy_finish(cs);

- err = pipe_buf_confirm(cs->pipe, buf);
- if (err)
- goto out_put_old;
-
BUG_ON(!cs->nr_segs);
cs->currbuf = buf;
cs->len = buf->len;
@@ -818,14 +790,6 @@ static int fuse_try_move_page(struct fuse_copy_state *cs, struct page **pagep)

newfolio = page_folio(buf->page);

- if (!folio_test_uptodate(newfolio))
- folio_mark_uptodate(newfolio);
-
- folio_clear_mappedtodisk(newfolio);
-
- if (fuse_check_folio(newfolio) != 0)
- goto out_fallback_unlock;
-
/*
* This is a new and locked page, it shouldn't be mapped or
* have any special flags on it
@@ -2020,7 +1984,6 @@ static ssize_t fuse_dev_splice_write(struct pipe_inode_info *pipe,
goto out_free;

*obuf = *ibuf;
- obuf->flags &= ~PIPE_BUF_FLAG_GIFT;
obuf->len = rem;
ibuf->offset += obuf->len;
ibuf->len -= obuf->len;
diff --git a/fs/pipe.c b/fs/pipe.c
index 2d88f73f585a..d5c86eb20f29 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -286,7 +286,6 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to)
struct pipe_buffer *buf = &pipe->bufs[tail & mask];
size_t chars = buf->len;
size_t written;
- int error;

if (chars > total_len) {
if (buf->flags & PIPE_BUF_FLAG_WHOLE) {
@@ -297,13 +296,6 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to)
chars = total_len;
}

- error = pipe_buf_confirm(pipe, buf);
- if (error) {
- if (!ret)
- ret = error;
- break;
- }
-
written = copy_page_to_iter(buf->page, buf->offset, chars, to);
if (unlikely(written < chars)) {
if (!ret)
@@ -462,10 +454,6 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)

if ((buf->flags & PIPE_BUF_FLAG_CAN_MERGE) &&
offset + chars <= PAGE_SIZE) {
- ret = pipe_buf_confirm(pipe, buf);
- if (ret)
- goto out;
-
ret = copy_page_from_iter(buf->page, offset, chars, from);
if (unlikely(ret < chars)) {
ret = -EFAULT;
diff --git a/fs/splice.c b/fs/splice.c
index 42af642c0ff8..2b1f109a7d4f 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -56,129 +56,6 @@ static noinline void noinline pipe_clear_nowait(struct file *file)
} while (!try_cmpxchg(&file->f_mode, &fmode, fmode & ~FMODE_NOWAIT));
}

-/*
- * Attempt to steal a page from a pipe buffer. This should perhaps go into
- * a vm helper function, it's already simplified quite a bit by the
- * addition of remove_mapping(). If success is returned, the caller may
- * attempt to reuse this page for another destination.
- */
-static bool page_cache_pipe_buf_try_steal(struct pipe_inode_info *pipe,
- struct pipe_buffer *buf)
-{
- struct folio *folio = page_folio(buf->page);
- struct address_space *mapping;
-
- folio_lock(folio);
-
- mapping = folio_mapping(folio);
- if (mapping) {
- WARN_ON(!folio_test_uptodate(folio));
-
- /*
- * At least for ext2 with nobh option, we need to wait on
- * writeback completing on this folio, since we'll remove it
- * from the pagecache. Otherwise truncate wont wait on the
- * folio, allowing the disk blocks to be reused by someone else
- * before we actually wrote our data to them. fs corruption
- * ensues.
- */
- folio_wait_writeback(folio);
-
- if (folio_has_private(folio) &&
- !filemap_release_folio(folio, GFP_KERNEL))
- goto out_unlock;
-
- /*
- * If we succeeded in removing the mapping, set LRU flag
- * and return good.
- */
- if (remove_mapping(mapping, folio)) {
- buf->flags |= PIPE_BUF_FLAG_LRU;
- return true;
- }
- }
-
- /*
- * Raced with truncate or failed to remove folio from current
- * address space, unlock and return failure.
- */
-out_unlock:
- folio_unlock(folio);
- return false;
-}
-
-static void page_cache_pipe_buf_release(struct pipe_inode_info *pipe,
- struct pipe_buffer *buf)
-{
- put_page(buf->page);
- buf->flags &= ~PIPE_BUF_FLAG_LRU;
-}
-
-/*
- * Check whether the contents of buf is OK to access. Since the content
- * is a page cache page, IO may be in flight.
- */
-static int page_cache_pipe_buf_confirm(struct pipe_inode_info *pipe,
- struct pipe_buffer *buf)
-{
- struct page *page = buf->page;
- int err;
-
- if (!PageUptodate(page)) {
- lock_page(page);
-
- /*
- * Page got truncated/unhashed. This will cause a 0-byte
- * splice, if this is the first page.
- */
- if (!page->mapping) {
- err = -ENODATA;
- goto error;
- }
-
- /*
- * Uh oh, read-error from disk.
- */
- if (!PageUptodate(page)) {
- err = -EIO;
- goto error;
- }
-
- /*
- * Page is ok afterall, we are done.
- */
- unlock_page(page);
- }
-
- return 0;
-error:
- unlock_page(page);
- return err;
-}
-
-const struct pipe_buf_operations page_cache_pipe_buf_ops = {
- .confirm = page_cache_pipe_buf_confirm,
- .release = page_cache_pipe_buf_release,
- .try_steal = page_cache_pipe_buf_try_steal,
- .get = generic_pipe_buf_get,
-};
-
-static bool user_page_pipe_buf_try_steal(struct pipe_inode_info *pipe,
- struct pipe_buffer *buf)
-{
- if (!(buf->flags & PIPE_BUF_FLAG_GIFT))
- return false;
-
- buf->flags |= PIPE_BUF_FLAG_LRU;
- return generic_pipe_buf_try_steal(pipe, buf);
-}
-
-static const struct pipe_buf_operations user_page_pipe_buf_ops = {
- .release = page_cache_pipe_buf_release,
- .try_steal = user_page_pipe_buf_try_steal,
- .get = generic_pipe_buf_get,
-};
-
static void wakeup_pipe_readers(struct pipe_inode_info *pipe)
{
smp_mb();
@@ -460,13 +337,6 @@ static int splice_from_pipe_feed(struct pipe_inode_info *pipe, struct splice_des
if (sd->len > sd->total_len)
sd->len = sd->total_len;

- ret = pipe_buf_confirm(pipe, buf);
- if (unlikely(ret)) {
- if (ret == -ENODATA)
- ret = 0;
- return ret;
- }
-
ret = actor(pipe, buf, sd);
if (ret <= 0)
return ret;
@@ -723,13 +593,6 @@ iter_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
continue;
this_len = min(this_len, left);

- ret = pipe_buf_confirm(pipe, buf);
- if (unlikely(ret)) {
- if (ret == -ENODATA)
- ret = 0;
- goto done;
- }
-
bvec_set_page(&array[n], buf->page, this_len,
buf->offset);
left -= this_len;
@@ -764,7 +627,7 @@ iter_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
}
}
}
-done:
+
kfree(array);
splice_from_pipe_end(pipe, &sd);

@@ -855,13 +718,6 @@ ssize_t splice_to_socket(struct pipe_inode_info *pipe, struct file *out,

seg = min_t(size_t, remain, buf->len);

- ret = pipe_buf_confirm(pipe, buf);
- if (unlikely(ret)) {
- if (ret == -ENODATA)
- ret = 0;
- break;
- }
-
bvec_set_page(&bvec[bc++], buf->page, seg, buf->offset);
remain -= seg;
if (remain == 0 || bc >= ARRAY_SIZE(bvec))
@@ -1450,7 +1306,6 @@ static int splice_try_to_steal_page(struct pipe_inode_info *pipe,
need_copy_unlock:
folio_unlock(folio);
need_copy:
-
copy = folio_alloc(GFP_KERNEL, 0);
if (!copy)
return -ENOMEM;
@@ -1578,10 +1433,6 @@ static long vmsplice_to_pipe(struct file *file, struct iov_iter *iter,
{
struct pipe_inode_info *pipe;
long ret = 0;
- unsigned buf_flag = 0;
-
- if (flags & SPLICE_F_GIFT)
- buf_flag = PIPE_BUF_FLAG_GIFT;

pipe = get_pipe_info(file, true);
if (!pipe)
@@ -1592,7 +1443,7 @@ static long vmsplice_to_pipe(struct file *file, struct iov_iter *iter,
pipe_lock(pipe);
ret = wait_for_space(pipe, flags);
if (!ret)
- ret = iter_to_pipe(iter, pipe, buf_flag);
+ ret = iter_to_pipe(iter, pipe, flags);
pipe_unlock(pipe);
if (ret > 0)
wakeup_pipe_readers(pipe);
@@ -1876,7 +1727,6 @@ static int splice_pipe_to_pipe(struct pipe_inode_info *ipipe,
* Don't inherit the gift and merge flags, we need to
* prevent multiple steals of this page.
*/
- obuf->flags &= ~PIPE_BUF_FLAG_GIFT;
obuf->flags &= ~PIPE_BUF_FLAG_CAN_MERGE;

obuf->len = len;
@@ -1968,7 +1818,6 @@ static int link_pipe(struct pipe_inode_info *ipipe,
* Don't inherit the gift and merge flag, we need to prevent
* multiple steals of this page.
*/
- obuf->flags &= ~PIPE_BUF_FLAG_GIFT;
obuf->flags &= ~PIPE_BUF_FLAG_CAN_MERGE;

if (obuf->len > len)
diff --git a/include/linux/pipe_fs_i.h b/include/linux/pipe_fs_i.h
index 02e0086b10f6..9cfbefd7ba31 100644
--- a/include/linux/pipe_fs_i.h
+++ b/include/linux/pipe_fs_i.h
@@ -6,7 +6,6 @@

#define PIPE_BUF_FLAG_LRU 0x01 /* page is on the LRU */
#define PIPE_BUF_FLAG_ATOMIC 0x02 /* was atomically mapped */
-#define PIPE_BUF_FLAG_GIFT 0x04 /* page is a gift */
#define PIPE_BUF_FLAG_PACKET 0x08 /* read() as a packet */
#define PIPE_BUF_FLAG_CAN_MERGE 0x10 /* can merge buffers */
#define PIPE_BUF_FLAG_WHOLE 0x20 /* read() must return entire buffer or error */
@@ -203,19 +202,6 @@ static inline void pipe_buf_release(struct pipe_inode_info *pipe,
ops->release(pipe, buf);
}

-/**
- * pipe_buf_confirm - verify contents of the pipe buffer
- * @pipe: the pipe that the buffer belongs to
- * @buf: the buffer to confirm
- */
-static inline int pipe_buf_confirm(struct pipe_inode_info *pipe,
- struct pipe_buffer *buf)
-{
- if (!buf->ops->confirm)
- return 0;
- return buf->ops->confirm(pipe, buf);
-}
-
/**
* pipe_buf_try_steal - attempt to take ownership of a pipe_buffer
* @pipe: the pipe that the buffer belongs to
diff --git a/include/linux/splice.h b/include/linux/splice.h
index 6c461573434d..3c5abbd49ff2 100644
--- a/include/linux/splice.h
+++ b/include/linux/splice.h
@@ -97,6 +97,5 @@ extern ssize_t splice_to_socket(struct pipe_inode_info *pipe, struct file *out,
extern int splice_grow_spd(const struct pipe_inode_info *, struct splice_pipe_desc *);
extern void splice_shrink_spd(struct splice_pipe_desc *);

-extern const struct pipe_buf_operations page_cache_pipe_buf_ops;
extern const struct pipe_buf_operations default_pipe_buf_ops;
#endif
diff --git a/mm/filemap.c b/mm/filemap.c
index a002df515966..dd144b0dab69 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2929,7 +2929,7 @@ ssize_t splice_folio_into_pipe(struct pipe_inode_info *pipe,
size_t part = min_t(size_t, PAGE_SIZE - offset, size - spliced);

*buf = (struct pipe_buffer) {
- .ops = &page_cache_pipe_buf_ops,
+ .ops = &default_pipe_buf_ops,
.page = page,
.offset = offset,
.len = part,

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