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From: Yu Ma <yu.ma@intel.com>
To: viro@zeniv.linux.org.uk,
	brauner@kernel.org,
	jack@suse.cz
Cc: linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	tim.c.chen@linux.intel.com,
	tim.c.chen@intel.com,
	pan.deng@intel.com,
	tianyou.li@intel.com,
	yu.ma@intel.com
Subject: [PATCH 2/3] fs/file.c: conditionally clear full_fds
Date: Fri, 14 Jun 2024 12:34:15 -0400
Message-ID: <20240614163416.728752-3-yu.ma@intel.com>
In-Reply-To: <20240614163416.728752-1-yu.ma@intel.com>
References: <20240614163416.728752-1-yu.ma@intel.com>
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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.
Together with patch 1, they improves pts/blogbench-1.1.0 read for 28%, and write
for 14% on Intel ICX 160 cores configuration with v6.8-rc6.

Reviewed-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Yu Ma <yu.ma@intel.com>
---
 fs/file.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/file.c b/fs/file.c
index e8d2f9ef7fd1..a0e94a178c0b 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -268,7 +268,9 @@ 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)
-- 
2.43.0