linux-kernel - Re: [PATCH v6 1/9] iversion: move inode_query

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Date:   Tue, 04 Oct 2022 10:05:59 +1100
From:   "NeilBrown" <neilb@...e.de>
To:     "Jeff Layton" <jlayton@...nel.org>
Cc:     tytso@....edu, adilger.kernel@...ger.ca, djwong@...nel.org,
        david@...morbit.com, trondmy@...merspace.com,
        viro@...iv.linux.org.uk, zohar@...ux.ibm.com, xiubli@...hat.com,
        chuck.lever@...cle.com, lczerner@...hat.com, jack@...e.cz,
        bfields@...ldses.org, brauner@...nel.org, fweimer@...hat.com,
        linux-btrfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, ceph-devel@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-nfs@...r.kernel.org,
        linux-xfs@...r.kernel.org
Subject: Re: [PATCH v6 1/9] iversion: move inode_query_iversion to libfs.c

On Fri, 30 Sep 2022, Jeff Layton wrote:
> There's no need to have such a large function forcibly inlined.
> 
> Signed-off-by: Jeff Layton <jlayton@...nel.org>

Reviewed-by: NeilBrown <neilb@...e.de>

you could possible make the "I_VERSION_QUERIED already set" case inline
and the "needs to be set" case out-of-line, but it probably isn't worth
it. 

Thanks,
NeilBrown


> ---
>  fs/libfs.c               | 36 ++++++++++++++++++++++++++++++++++++
>  include/linux/iversion.h | 38 ++------------------------------------
>  2 files changed, 38 insertions(+), 36 deletions(-)
> 
> diff --git a/fs/libfs.c b/fs/libfs.c
> index 682d56345a1c..5ae81466a422 100644
> --- a/fs/libfs.c
> +++ b/fs/libfs.c
> @@ -1566,3 +1566,39 @@ bool inode_maybe_inc_iversion(struct inode *inode, bool force)
>  	return true;
>  }
>  EXPORT_SYMBOL(inode_maybe_inc_iversion);
> +
> +/**
> + * inode_query_iversion - read i_version for later use
> + * @inode: inode from which i_version should be read
> + *
> + * Read the inode i_version counter. This should be used by callers that wish
> + * to store the returned i_version for later comparison. This will guarantee
> + * that a later query of the i_version will result in a different value if
> + * anything has changed.
> + *
> + * In this implementation, we fetch the current value, set the QUERIED flag and
> + * then try to swap it into place with a cmpxchg, if it wasn't already set. If
> + * that fails, we try again with the newly fetched value from the cmpxchg.
> + */
> +u64 inode_query_iversion(struct inode *inode)
> +{
> +	u64 cur, new;
> +
> +	cur = inode_peek_iversion_raw(inode);
> +	do {
> +		/* If flag is already set, then no need to swap */
> +		if (cur & I_VERSION_QUERIED) {
> +			/*
> +			 * This barrier (and the implicit barrier in the
> +			 * cmpxchg below) pairs with the barrier in
> +			 * inode_maybe_inc_iversion().
> +			 */
> +			smp_mb();
> +			break;
> +		}
> +
> +		new = cur | I_VERSION_QUERIED;
> +	} while (!atomic64_try_cmpxchg(&inode->i_version, &cur, new));
> +	return cur >> I_VERSION_QUERIED_SHIFT;
> +}
> +EXPORT_SYMBOL(inode_query_iversion);
> diff --git a/include/linux/iversion.h b/include/linux/iversion.h
> index e27bd4f55d84..6755d8b4f20b 100644
> --- a/include/linux/iversion.h
> +++ b/include/linux/iversion.h
> @@ -234,42 +234,6 @@ inode_peek_iversion(const struct inode *inode)
>  	return inode_peek_iversion_raw(inode) >> I_VERSION_QUERIED_SHIFT;
>  }
>  
> -/**
> - * inode_query_iversion - read i_version for later use
> - * @inode: inode from which i_version should be read
> - *
> - * Read the inode i_version counter. This should be used by callers that wish
> - * to store the returned i_version for later comparison. This will guarantee
> - * that a later query of the i_version will result in a different value if
> - * anything has changed.
> - *
> - * In this implementation, we fetch the current value, set the QUERIED flag and
> - * then try to swap it into place with a cmpxchg, if it wasn't already set. If
> - * that fails, we try again with the newly fetched value from the cmpxchg.
> - */
> -static inline u64
> -inode_query_iversion(struct inode *inode)
> -{
> -	u64 cur, new;
> -
> -	cur = inode_peek_iversion_raw(inode);
> -	do {
> -		/* If flag is already set, then no need to swap */
> -		if (cur & I_VERSION_QUERIED) {
> -			/*
> -			 * This barrier (and the implicit barrier in the
> -			 * cmpxchg below) pairs with the barrier in
> -			 * inode_maybe_inc_iversion().
> -			 */
> -			smp_mb();
> -			break;
> -		}
> -
> -		new = cur | I_VERSION_QUERIED;
> -	} while (!atomic64_try_cmpxchg(&inode->i_version, &cur, new));
> -	return cur >> I_VERSION_QUERIED_SHIFT;
> -}
> -
>  /*
>   * For filesystems without any sort of change attribute, the best we can
>   * do is fake one up from the ctime:
> @@ -283,6 +247,8 @@ static inline u64 time_to_chattr(struct timespec64 *t)
>  	return chattr;
>  }
>  
> +u64 inode_query_iversion(struct inode *inode);
> +
>  /**
>   * inode_eq_iversion_raw - check whether the raw i_version counter has changed
>   * @inode: inode to check
> -- 
> 2.37.3
> 
>