From: Christoph Hellwig <hch@infradead.org>
To: "Darrick J. Wong" <djwong@kernel.org>
Cc: zlang@redhat.com, linux-xfs@vger.kernel.org,
fstests@vger.kernel.org, guan@eryu.me,
linux-block@vger.kernel.org, linux-scsi@vger.kernel.org
Subject: Re: [PATCH 1/3] xfs/178: don't fail when SCRATCH_DEV contains random xfs superblocks
Date: Tue, 10 Oct 2023 00:01:33 -0700 [thread overview]
Message-ID: <ZST2zRvtMrU0KlkN@infradead.org> (raw)
In-Reply-To: <169687551395.3948976.8425812597156927952.stgit@frogsfrogsfrogs>
On Mon, Oct 09, 2023 at 11:18:33AM -0700, Darrick J. Wong wrote:
> The storage advertises SCSI UNMAP support, but it is of the variety
> where the UNMAP command returns immediately but takes its time to unmap
> in the background. Subsequent rereads are allowed to return stale
> contents, per DISCARD semantics.
>
> When the fstests cloud is not busy, the old contents disappear in a few
> seconds. However, at peak utilization, there are ~75 VMs running, and
> the storage backend can take several minutes to commit these background
> requests.
Umm, that is not valid behavior fo SCSI UNMAP or any other command
that Linux discard maps to. All of them can do one of the two options
on a per-block basis:
- return the unmap pattern (usually but not always 0) for any read
following the unmap/trim/discard
- always return the previous pattern until it is overwritten or
discarded again
Changing the pattern some time after unmap is a grave bug, and we need
to blacklist the device.
next prev parent reply other threads:[~2023-10-10 7:01 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-09 18:18 [PATCHSET 0/3] fstests: random fixes for v2023.10.08 Darrick J. Wong
2023-10-09 18:18 ` [PATCH 1/3] xfs/178: don't fail when SCRATCH_DEV contains random xfs superblocks Darrick J. Wong
2023-10-10 7:01 ` Christoph Hellwig [this message]
2023-10-11 19:10 ` Darrick J. Wong
2023-10-12 4:26 ` Christoph Hellwig
2023-10-12 5:03 ` Darrick J. Wong
2023-10-12 8:30 ` Christoph Hellwig
2023-10-12 15:09 ` [PATCH v2 " Darrick J. Wong
2023-10-12 15:10 ` Christoph Hellwig
2023-10-09 18:18 ` [PATCH 2/3] generic/465: only complain about stale disk contents when racing directio Darrick J. Wong
2023-10-10 7:03 ` Christoph Hellwig
2023-10-09 18:18 ` [PATCH 3/3] generic/269,xfs/051: don't drop fsstress failures to stdout Darrick J. Wong
2023-10-10 7:03 ` Christoph Hellwig
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