pipe: don't update {a,c,m}time for anonymous pipes

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>
Link: https://lore.kernel.org/r/20250205181812.GC13817@redhat.com
Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/pipe.c b/fs/pipe.c
index 2eacfde61e745f0dcbe77ff768f906dd3aeb3771..2ae75adfba64bdcd87a3f759fa4b84d82c09fc5e 100644 (file)
--- 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 @@ out:
        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;
 }
@@ -1234,8 +1251,8 @@ err:
 
 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,
@@ -1245,8 +1262,8 @@ const struct file_operations pipefifo_fops = {
 
 static 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,