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Wed, 21 Oct 2026 09:26:47 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id Th/GMleF2GorEgAAD6G6ig (envelope-from ); Wed, 21 Oct 2026 09:26:47 +0000 Message-ID: <22f965be-ed14-4e70-a332-46c092898eea@suse.de> Date: Wed, 21 Oct 2026 11:26:47 +0200 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 2/3] dm zoned: do not reclaim a random zone into another random zone To: Kyrylo Biryuk , dm-devel@lists.linux.dev Cc: agk@redhat.com, snitzer@kernel.org, mpatocka@redhat.com, bmarzins@redhat.com, dlemoal@kernel.org, linux-kernel@vger.kernel.org References: <20261011175450.952-1-illofspeed@gmail.com> <20261011175450.952-3-illofspeed@gmail.com> Content-Language: en-US From: Hannes Reinecke In-Reply-To: <20261011175450.952-3-illofspeed@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Spamd-Result: default: False [-4.29 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; XM_UA_NO_VERSION(0.01)[]; RCPT_COUNT_SEVEN(0.00)[8]; FREEMAIL_TO(0.00)[gmail.com,lists.linux.dev]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; ARC_NA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; MIME_TRACE(0.00)[0:+]; MID_RHS_MATCH_FROM(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; RCVD_TLS_ALL(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:email,imap1.dmz-prg2.suse.org:helo] X-Spam-Score: -4.29 X-Spam-Level: X-Spam-Flag: NO On 10/11/26 7:54 PM, Kyrylo Biryuk wrote: > dmz_reclaim_rnd_data() falls back to a random destination zone when no > free sequential zone is available and the target has cache zones. When > the target is idle and the cache zone list is empty, > dmz_get_rnd_zone_for_reclaim() selects random zones of the zoned device > as well, so a random zone is then copied into another random zone. That > frees nothing: the next pass picks the next random zone and copies it > again, for as long as the target stays idle. > > Seen on a two-device target (256 GiB regular cache device plus a 27 TB > host-managed drive) used as an md RAID5 member: after a full rebuild > every chunk was mapped and no sequential zone was free, and the idle > drive read and wrote about 72 MB/s each without pause for hours while > the free zone counters in "dmsetup status" did not change. Reproduced on > emulated host-managed drives (tcmu-runner ZBC handler): 340 MB/s of > copying on an idle target, 0 MB/s with this patch. > > Only switch to a random destination zone when the zone being reclaimed > is a cache zone: moving it to the zoned device still frees cache space. > > Fixes: c5c788595292 ("dm zoned: start reclaim with sequential zones") > Assisted-by: LLM > Signed-off-by: Kyrylo Biryuk > --- > drivers/md/dm-zoned-reclaim.c | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > diff --git a/drivers/md/dm-zoned-reclaim.c b/drivers/md/dm-zoned-reclaim.c > index 315f0da99f3..88d56d3c86d 100644 > --- a/drivers/md/dm-zoned-reclaim.c > +++ b/drivers/md/dm-zoned-reclaim.c > @@ -288,7 +288,13 @@ static int dmz_reclaim_rnd_data(struct dmz_reclaim *zrc, struct dm_zone *dzone) > again: > szone = dmz_alloc_zone(zmd, zrc->dev_idx, > alloc_flags | DMZ_ALLOC_RECLAIM); > - if (!szone && alloc_flags == DMZ_ALLOC_SEQ && dmz_nr_cache_zones(zmd)) { > + /* > + * If no free sequential zone is available, a cache zone can still be > + * moved into a free random zone of the zoned device, which frees cache > + * space. Do not do this for a random zone: moving it into another > + * random zone frees nothing and, on an idle target, repeats forever. > + */ > + if (!szone && alloc_flags == DMZ_ALLOC_SEQ && dmz_is_cache(dzone)) { > alloc_flags = DMZ_ALLOC_RND; > goto again; > } Reviewed-by: Hannes Reinecke Cheers, Hannes -- Dr. Hannes Reinecke Kernel Storage Architect hare@suse.de +49 911 74053 688 SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich