Re: [RFC PATCH v2] f2fs: map data writes to FDP streams

[Chao Yu]

On 4/17/2026 11:51 AM, Wenjie Qi wrote:
> From: Wenjie Qi <qwjhust@xxxxxxxxx>
>
> From: Wenjie Qi <qiwenjie@xxxxxxxxxx>
>
> F2FS already classifies DATA writes using its existing hot, warm and cold
> temperature policy, but it only passes that intent down as a write hint.
> That hint alone is not sufficient for NVMe FDP placement, because the
> current NVMe command path consumes `bio->bi_write_stream` rather than
> `bio->bi_write_hint` when selecting a placement ID.
>
> When the target block device exposes write streams, map the existing F2FS
> DATA temperature classes onto stream IDs and set `bio->bi_write_stream`
> for both buffered and direct writes. If the device exposes no write
> streams, keep the current behavior by leaving the stream unset.
>
> The stream mapping is evaluated against the target block device of each
> bio, so the existing per-device fallback behavior stays unchanged for
> multi-device filesystems. Existing blkzoned restrictions also remain in
> place.
>
> The mapping is intentionally small and deterministic:
>
> - 1 stream: hot, warm and cold all use stream 1
> - 2 streams: hot/warm use 1, cold uses 2
> - 3+ streams: hot uses 1, warm uses 2, cold uses 3
>
> Signed-off-by: Wenjie Qi <qwjhust@xxxxxxxxx>

Reviewed-by: Chao Yu <chao@xxxxxxxxxx>

Thanks,