Re: [PATCH v5 0/4] dm zoned: fix idle reclaim problems

[Mikulas Patocka <mpatocka@redhat.com>]

On Tue, 13 Oct 2026, Kyrylo Biryuk wrote:

> Mikulas,
> 
> I noticed too late that v3 of this series is already in dm-7.4 and
> for-next (24646f6ed3, 2cca719c63, 5829edd027), so v4 crossed with it.
> This v5 is v4 plus one more fix; if you prefer to keep v3, I can send
> the v4 changes and patch 4 as incremental patches on top of dm-7.4
> instead - please tell me which you want.

Hi

Linus doesn't want development being done close to the start of the merge 
window (or during the merge window), so I reverted the patches from my 
tree and I will postpone them.

I suggest - separate the patches into bugfixes (they have the "Fixes:" 
line and the "Cc: stable@vger.kernel.org" line) and performance 
enhancements (without "Fixes:" and "Cc: stable@vger.kernel.org"). The 
bugfixes may go in later during the 7.4 cycle, the performance 
enhancements will wait for the 7.5 merge window.

Mikulas

> Patch 4 is new. While measuring an idle pool I found that an idle
> target whose random (and cache) zones are all free never stops running
> its reclaim work: since 90a9b8693f1b ("dm zoned: reclaim random zones
> when idle"), dmz_should_reclaim() treats "idle" plus a non-zero total
> number of random zones as "reclaim now", dmz_do_reclaim() finds no
> candidate and returns -EBUSY, dmz_check_dev() checks every device for
> media events (a TEST UNIT READY on SCSI disks), and the work is requeued
> with no delay. In mainline the loop can end when a pass finishes while
> the target is busy with enough free zones; with patch 3 the idle poll
> stays armed, so the loop recurs whenever the target becomes idle.
> 
> Measured on 7.3-rc7 with three emulated host-managed members of an md
> RAID5 (idle, 30 s average):
> 
>   stock dm-zoned        181,195 SCSI commands/s   32 % kernel CPU
>   v4 (patches 1-3)      187,707 SCSI commands/s   31 % kernel CPU
>   v5 (patches 1-4)            0 SCSI commands/s    0 % kernel CPU
> 
> With patch 4, the random zones filled by a 2 GiB write burst are still
> reclaimed once the target is idle, and on three 27 TB host-managed
> drives (7.2.10 with these patches) an idle pool went from about 155,000
> TEST UNIT READY commands per second per drive to none.
> 
> Changes since v4:
>  - new patch 4 (above)
>  - patch 3: Reviewed-by from Damien Le Moal
>  - patches 1-3 otherwise unchanged
> 
> Kyrylo Biryuk (4):
>   dm zoned: back off when reclaim finds no destination zone
>   dm zoned: do not reclaim a random zone into another random zone
>   dm zoned: keep polling for idle reclaim after a reclaim pass
>   dm zoned: do not busy-loop idle reclaim when no zone needs reclaim
> 
>  drivers/md/dm-zoned-reclaim.c | 31 ++++++++++++++++++++++++++-----
>  1 file changed, 26 insertions(+), 5 deletions(-)
>