linux-kernel - Thin pool CoW latency

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Date:   Sun, 5 Mar 2023 15:40:02 -0500
From:   Demi Marie Obenour <demi@...isiblethingslab.com>
To:     Joe Thornber <thornber@...hat.com>
Cc:     "development, device-mapper" <dm-devel@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Marek Marczykowski-Górecki 
        <marmarek@...isiblethingslab.com>,
        Qubes OS Development Mailing List 
        <qubes-devel@...glegroups.com>, dm-devel@...ts.ewheeler.net
Subject: Thin pool CoW latency

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Like Eric, I am very concerned about CoW latency and throughput.  I
am almost certain that allocating new blocks and snapshot copy-on-write
are _the_ hot paths in Qubes OS.  In particular, I suspect that
workloads such as building an image in a throwaway VM or installing
packages onto a root volume that had just been shapshotted are dominated
by metadata operations, rather than by in-place updates.  I suspect that
frequently-snapshotted volumes will observe similar behavior in general.
- -- 
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab
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