From: Andrey Zhadchenko <andrey.zhadchenko@virtuozzo.com>
To: khorenko@virtuozzo.com, alexander.ivanov@virtuozzo.com
Cc: devel@openvz.org
Subject: [Devel] [PATCH hci-8.1 0/2] dm-qcow2, dm-ploop: do not merge discards with gaps
Date: Mon, 9 Nov 2026 18:36:17 +0300 [thread overview]
Message-ID: <20261109153619.277888-1-andrey.zhadchenko@virtuozzo.com> (raw)
The block layer may merge non-contiguous discard bios into a single
request when the queue allows more than one discard segment, and the
stacking default for dm is max_discard_segments = USHRT_MAX.
Both dm-qcow2 and dm-ploop handle a discard request as one contiguous
range taken from blk_rq_pos() and blk_rq_bytes(). For a request built
from bios [0, 512) and [1024, 1536) they discard [0, 1024), which hits
sectors that were never asked to be discarded and misses part of the
range that was.
Set max_discard_segments to 1 in both targets so each discard request
always describes a single contiguous range.
https://virtuozzo.atlassian.net/browse/VSTOR-154159
Andrey Zhadchenko (2):
dm-qcow2: set max discard segments to one
dm-ploop: set max discard segments to one
drivers/md/dm-ploop-target.c | 1 +
drivers/md/dm-qcow2-target.c | 1 +
2 files changed, 2 insertions(+)
--
2.43.5
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next reply other threads:[~2026-11-09 15:42 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-11-09 15:36 Andrey Zhadchenko [this message]
2026-11-09 15:36 ` [Devel] [PATCH hci-8.1 1/2] dm-qcow2: set max discard segments to one Andrey Zhadchenko
2026-11-09 15:44 ` no-reply
2026-11-09 15:36 ` [Devel] [PATCH hci-8.1 2/2] dm-ploop: " Andrey Zhadchenko
2026-11-09 15:44 ` no-reply
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