On 12/21/20 10:49 PM, Naohiro Aota wrote:

If more than one IO is issued for one file extent, these IO can be written
to separate regions on a device. Since we cannot map one file extent to
such a separate area, we need to follow the "one IO == one ordered extent"
rule.

The Normal buffered, uncompressed, not pre-allocated write path (used by
cow_file_range()) sometimes does not follow this rule. It can write a part
of an ordered extent when specified a region to write e.g., when its
called from fdatasync().

Introduces a dedicated (uncompressed buffered) data write path for ZONED
mode. This write path will CoW the region and write it at once.

Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>

This means we'll write one page at a time, no coalescing of data pages.  I'm not 
the one with zoned devices in production, but it might be worth fixing this in 
the future so you're not generating a billion bio's for large sequential data areas.

Reviewed-by: Josef Bacik <josef@toxicpanda.com>

Thanks,

Josef