linux-kernel - Re: [PATCH v2 2/3] fs/file.c: conditionally clear full

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Message-ID: <20240625115442.kkrqy6yvy6qpct4y@quack3>
Date: Tue, 25 Jun 2024 13:54:42 +0200
From: Jan Kara <jack@...e.cz>
To: Yu Ma <yu.ma@...el.com>
Cc: viro@...iv.linux.org.uk, brauner@...nel.org, jack@...e.cz,
	mjguzik@...il.com, edumazet@...gle.com,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	pan.deng@...el.com, tianyou.li@...el.com, tim.c.chen@...el.com,
	tim.c.chen@...ux.intel.com
Subject: Re: [PATCH v2 2/3] fs/file.c: conditionally clear full_fds

On Sat 22-06-24 11:49:03, Yu Ma wrote:
> 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 27%, and write
> for 14% on Intel ICX 160 cores configuration with v6.10-rc4.
> 
> Reviewed-by: Tim Chen <tim.c.chen@...ux.intel.com>
> Signed-off-by: Yu Ma <yu.ma@...el.com>

Nice. Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/file.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/file.c b/fs/file.c
> index 50e900a47107..b4d25f6d4c19 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 inline bool fd_is_open(unsigned int fd, const struct fdtable *fdt)
> -- 
> 2.43.0
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR