Re: [PATCH 04/13] block: Restore write hint support

[Bart Van Assche <bvanassche@acm.org>]

On 10/2/23 04:23, Avri Altman wrote:
>> The following aspects of that commit have been dropped:
>> - Debugfs support for retrieving and modifying write hints.
> 
> Any particular reason to left those out?

The above comment is misleading: what has not been restored is the
struct request_queue write_hints[] array member nor the debugfs
interface for accessing that array. My understanding is that that array
was used to track stream statistics by the NVMe driver. From version
v5.17 of the NVMe driver:

	if (streamid < ARRAY_SIZE(req->q->write_hints))
		req->q->write_hints[streamid] += blk_rq_bytes(req) >> 9;

>> - md-raid, BTRFS, ext4, gfs2 and zonefs write hint support.
> 
> Native Linux with ext4 is being used in automotive, and even mobile
> platforms. E.g. Qualcomm's RB5 is formally maintained with Debian -
> https://releases.linaro.org/96boards/rb5/linaro/debian/21.12/

All ext4 did with write hint information is to copy the inode write
hint information into the bio. The inode write hint information is set
by the F_SET_RW_HINT fcntl. The only software packages that use the
F_SET_RW_HINT fcntl and that I'm aware of are RocksDB, Samba, stress_ng
and rr. Are any of these software packages used in automotive software
on top of ext4?

Thanks,

Bart.