Re: [PATCH] xfs: update BDI {io,ra}_pages values based on the RT device limits

On 7/20/26 23:08, Christoph Hellwig wrote:
> When using XFS with a main device on an SSD that stores metadata and a RT
> device to store data on a HDD, we fail to take the I/O sizes for the RT
> device into accounting, leading to up to 5% slower read performance when
> using an SSD for metadata vs storing data and metadata on the HDD.
> 
> Fix this up by taking the RT settings into account at mount an restoring
> the old settings at unmount time, unless the BDI settings have changed
> from those set by XFS.
> 
> Reported-by: Filip Blagojevic <[email protected]>
> Signed-off-by: Christoph Hellwig <[email protected]>

[...]

> +/*
> + * When using a RT device some or all data I/O is using the RT device, but
> + * the BDI is inherited from the main data device.  When the underlying block
> + * device for the RT device has larger I/O sizes, the BDI settings might be
> + * incorrect, which is especially bad if the main device is a SSD and the
> + * RT device is a HDD, as the io_opt fixup in blk_apply_bdi_limits is missing
> + * for this case.
> + *
> + * Update the BDI values to the max of the data and RT device to cover our

s/data/main ?
I am still confused about the proper name for the device holding metadata :)

Other than this, this looks OK to me.

Reviewed-by: Damien Le Moal <[email protected]>


-- 
Damien Le Moal
Western Digital Research