Re: [PATCH] fs: fix forced iversion increment on lazytime timestamp updates

[Jeff Layton <jlayton@kernel.org>]

On Mon, 2026-05-11 at 13:19 +0200, Pankaj Raghav wrote:
> When updating timestamps with lazytime enabled, if only I_DIRTY_TIME is
> set (pure lazytime update), inode_maybe_inc_iversion() should not be
> forced to increment i_version. The force parameter should only be true
> when actual data or metadata changes require an iversion bump.
> 
> The current code uses "!!dirty" which evaluates to true whenever dirty
> has any bits set, including the I_DIRTY_TIME bit alone. This forces an
> iversion increment on every lazytime timestamp update, which then sets
> I_DIRTY_SYNC, triggering expensive log flushes on subsequent fdatasync
> calls. Andres reported this issue when he noticed a perf regression[1].
> 
> Fix this by using "dirty != I_DIRTY_TIME" as the force parameter. This
> passes false for pure lazytime updates (allowing the I_VERSION_QUERIED
> optimization to work), while still forcing the increment when dirty
> contains other flags indicating real changes that require iversion
> updates.
> 
> [1] https://lore.kernel.org/linux-xfs/7ys6erh3nnyeerv2nybyfvp7dmaknuxrlxv74wx56ocdothkc6@ekfiadtkfn2r/
> 
> Fixes: 85c871a02b03 ("fs: add support for non-blocking timestamp updates")
> Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
> ---
>  fs/inode.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/inode.c b/fs/inode.c
> index 6a3cbc7dcd28..62c579a0cf7d 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -2124,7 +2124,13 @@ static int inode_update_cmtime(struct inode *inode, unsigned int flags)
>  			    inode_iversion_need_inc(inode))
>  				return -EAGAIN;
>  		} else {
> -			if (inode_maybe_inc_iversion(inode, !!dirty))
> +			/*
> +			 * Don't force iversion increment for pure lazytime
> +			 * updates (I_DIRTY_TIME only), let I_VERSION_QUERIED
> +			 * dictate whether the increment is needed.
> +			 */
> +			if (inode_maybe_inc_iversion(inode,
> +						     dirty != I_DIRTY_TIME))
>  				dirty |= I_DIRTY_SYNC;
>  		}
>  	}
> 
> base-commit: 4cd074ae20bbcc293bbbce9163abe99d68ae6ae0

Reviewed-by: Jeff Layton <jlayton@kernel.org>