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 fc90888d07b8
("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>

diff --git a/fs/file.c b/fs/file.c
index 90b8aa2378cc20fad9a8a112b36c3b6263aa1873..36c5089812f5776085ae753219b31876dcb7fb3a 100644 (file)
--- a/fs/file.c
+++ b/fs/file.c
@@ -264,7 +264,9 @@ 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 inline bool fd_is_open(unsigned int fd, const struct fdtable *fdt)