Re: [PATCH 25/26] block: Reduce zone write plugging memory usage

[Damien Le Moal <dlemoal@kernel.org>]

On 2/7/24 06:20, Bart Van Assche wrote:
> On 2/5/24 15:55, Damien Le Moal wrote:
>> The array of struct blk_zone_wplug for the disk is sized for the total number of
>> zones of the drive. The reason for that is that we want to retain the wp_offset
>> value for all zones, even if they are not being written. Otherwise, everytime we
>> start writing a zone, we would need to do a report zones to be able to emulate
>> zone append operations if the drive requested that.
> 
> We do not need to track wp_offset for empty zones nor for full zones. The data
> structure with plug information would become a lot smaller if it only tracks
> information for zones that are neither empty nor full. If a zone append is
> submitted to a zone and no information is being tracked for that zone, we can
> initialize wp_offset to zero. That may not match the actual write pointer if
> the zone is full but that shouldn't be an issue since write appends submitted
> to a zone that is full fail anyway.

We still need to keep in memory the write pointer offset of zones that are not
being actively written to but have been previously partially written. So I do
not see how excluding empty and full zones from that tracking simplifies
anything at all. And the union of wp offset+zone capacity with a pointer to the
active zone plug structure is not *that* complicated to handle...

-- 
Damien Le Moal
Western Digital Research