fs/file.c: conditionally clear full_fds

JIRA: https://issues.redhat.com/browse/RHEL-38570
Upstream status: Linus

commit c9a3019
Author: Yu Ma <yu.ma@intel.com>
Date:   Wed Jul 17 10:50:17 2024 -0400

    fs/file.c: conditionally clear full_fds

    64 bits in open_fds are mapped to a common bit in full_fds_bits. It is very
    likely that a bit in full_fds_bits has been cleared before in
    __clear_open_fds()'s operation. Check the clear bit in full_fds_bits before
    clearing to avoid unnecessary write and cache bouncing. See commit fc90888
    ("vfs: conditionally clear close-on-exec flag") for a similar optimization.
    take stock kernel with patch 1 as baseline, it improves pts/blogbench-1.1.0
    read for 13%, and write for 5% on Intel ICX 160 cores configuration with
    v6.10-rc7.

    Reviewed-by: Jan Kara <jack@suse.cz>
    Reviewed-by: Tim Chen <tim.c.chen@linux.intel.com>
    Signed-off-by: Yu Ma <yu.ma@intel.com>
    Link: https://lore.kernel.org/r/20240717145018.3972922-3-yu.ma@intel.com
    Signed-off-by: Christian Brauner <brauner@kernel.org>
    Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Signed-off-by: Ian Kent <ikent@redhat.com>

Author: Ian Kent

fs/file.c

@@ -252,7 +252,9 @@ static inline void __set_open_fd(unsigned int fd, struct fdtable *fdt)
 static inline void __clear_open_fd(unsigned int fd, struct fdtable *fdt)
 {
 	__clear_bit(fd, fdt->open_fds);
-	__clear_bit(fd / BITS_PER_LONG, fdt->full_fds_bits);
+	fd /= BITS_PER_LONG;
+	if (test_bit(fd, fdt->full_fds_bits))
+		__clear_bit(fd, fdt->full_fds_bits);
 }
 
 static unsigned int count_open_files(struct fdtable *fdt)