[PATCH v2 2/2] pipe: don't update {a,c,m}time for anonymous pipes

Oleg Nesterov
2025-02-05T15:34:30Z

These numbers are visible in fstat() but hopefully nobody uses this
information and file_accessed/file_update_time are not that cheap.
Stupid test-case:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <assert.h>
#include <sys/ioctl.h>
#include <sys/time.h>

static char buf[17 * 4096];
static struct timeval TW, TR;

int wr(int fd, int size)
{
int c, r;
struct timeval t0, t1;

gettimeofday(&t0, NULL);
for (c = 0; (r = write(fd, buf, size)) > 0; c += r);
gettimeofday(&t1, NULL);
timeradd(&TW, &t1, &TW);
timersub(&TW, &t0, &TW);

return c;
}

int rd(int fd, int size)
{
int c, r;
struct timeval t0, t1;

gettimeofday(&t0, NULL);
for (c = 0; (r = read(fd, buf, size)) > 0; c += r);
gettimeofday(&t1, NULL);
timeradd(&TR, &t1, &TR);
timersub(&TR, &t0, &TR);

return c;
}

int main(int argc, const char *argv[])
{
int fd[2], nb = 1, loop, size;

assert(argc == 3);
loop = atoi(argv[1]);
size = atoi(argv[2]);

assert(pipe(fd) == 0);
assert(ioctl(fd[0], FIONBIO, &nb) == 0);
assert(ioctl(fd[1], FIONBIO, &nb) == 0);

assert(size <= sizeof(buf));
while (loop--)
assert(wr(fd[1], size) == rd(fd[0], size));

struct timeval tt;
timeradd(&TW, &TR, &tt);
printf("TW = %lu.%03lu TR = %lu.%03lu TT = %lu.%03lu\n",
TW.tv_sec, TW.tv_usec/1000,
TR.tv_sec, TR.tv_usec/1000,
tt.tv_sec, tt.tv_usec/1000);

return 0;
}

Before:
# for i in 1 2 3; do /host/tmp/test 10000 100; done
TW = 8.047 TR = 5.845 TT = 13.893
TW = 8.091 TR = 5.872 TT = 13.963
TW = 8.083 TR = 5.885 TT = 13.969
After:
# for i in 1 2 3; do /host/tmp/test 10000 100; done
TW = 4.752 TR = 4.664 TT = 9.416
TW = 4.684 TR = 4.608 TT = 9.293
TW = 4.736 TR = 4.652 TT = 9.388

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
fs/pipe.c | 41 +++++++++++++++++++++++++++++------------
1 file changed, 29 insertions(+), 12 deletions(-)

diff --git a/fs/pipe.c b/fs/pipe.c
index b05cded28d9b..e772637c622c 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -248,7 +248,7 @@ static inline unsigned int pipe_update_tail(struct pipe_inode_info *pipe,
}

static ssize_t
-pipe_read(struct kiocb *iocb, struct iov_iter *to)
+anon_pipe_read(struct kiocb *iocb, struct iov_iter *to)
{
size_t total_len = iov_iter_count(to);
struct file *filp = iocb->ki_filp;
@@ -404,8 +404,15 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to)
if (wake_next_reader)
wake_up_interruptible_sync_poll(&pipe->rd_wait, EPOLLIN | EPOLLRDNORM);
kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
+ return ret;
+}
+
+static ssize_t
+fifo_pipe_read(struct kiocb *iocb, struct iov_iter *to)
+{
+ int ret = anon_pipe_read(iocb, to);
if (ret > 0)
- file_accessed(filp);
+ file_accessed(iocb->ki_filp);
return ret;
}

@@ -426,7 +433,7 @@ static inline bool pipe_writable(const struct pipe_inode_info *pipe)
}

static ssize_t
-pipe_write(struct kiocb *iocb, struct iov_iter *from)
+anon_pipe_write(struct kiocb *iocb, struct iov_iter *from)
{
struct file *filp = iocb->ki_filp;
struct pipe_inode_info *pipe = filp->private_data;
@@ -604,11 +611,21 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
if (wake_next_writer)
wake_up_interruptible_sync_poll(&pipe->wr_wait, EPOLLOUT | EPOLLWRNORM);
- if (ret > 0 && sb_start_write_trylock(file_inode(filp)->i_sb)) {
- int err = file_update_time(filp);
- if (err)
- ret = err;
- sb_end_write(file_inode(filp)->i_sb);
+ return ret;
+}
+
+static ssize_t
+fifo_pipe_write(struct kiocb *iocb, struct iov_iter *from)
+{
+ int ret = anon_pipe_write(iocb, from);
+ if (ret > 0) {
+ struct file *filp = iocb->ki_filp;
+ if (sb_start_write_trylock(file_inode(filp)->i_sb)) {
+ int err = file_update_time(filp);
+ if (err)
+ ret = err;
+ sb_end_write(file_inode(filp)->i_sb);
+ }
}
return ret;
}
@@ -1232,8 +1249,8 @@ static int fifo_open(struct inode *inode, struct file *filp)

const struct file_operations pipefifo_fops = {
.open = fifo_open,
- .read_iter = pipe_read,
- .write_iter = pipe_write,
+ .read_iter = fifo_pipe_read,
+ .write_iter = fifo_pipe_write,
.poll = pipe_poll,
.unlocked_ioctl = pipe_ioctl,
.release = pipe_release,
@@ -1243,8 +1260,8 @@ const struct file_operations pipefifo_fops = {

const struct file_operations pipeanon_fops = {
.open = fifo_open,
- .read_iter = pipe_read,
- .write_iter = pipe_write,
+ .read_iter = anon_pipe_read,
+ .write_iter = anon_pipe_write,
.poll = pipe_poll,
.unlocked_ioctl = pipe_ioctl,
.release = pipe_release,
--
2.25.1.362.g51ebf55