Commit 64b1a728 authored by mulhern's avatar mulhern Committed by Greg Kroah-Hartman

dm thin: fix documentation relative to low water mark threshold

[ Upstream commit 9b28a110 ]

Fixes:
1. The use of "exceeds" when the opposite of exceeds, falls below,
was meant.
2. Properly speaking, a table can not exceed a threshold.

It emphasizes the important point, which is that it is the userspace
daemon's responsibility to check for low free space when a device
is resumed, since it won't get a special event indicating low free
space in that situation.
Signed-off-by: 's avatarmulhern <amulhern@redhat.com>
Signed-off-by: 's avatarMike Snitzer <snitzer@redhat.com>
Signed-off-by: 's avatarSasha Levin <alexander.levin@microsoft.com>
Signed-off-by: 's avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent b5c2e607
......@@ -112,9 +112,11 @@ $low_water_mark is expressed in blocks of size $data_block_size. If
free space on the data device drops below this level then a dm event
will be triggered which a userspace daemon should catch allowing it to
extend the pool device. Only one such event will be sent.
Resuming a device with a new table itself triggers an event so the
userspace daemon can use this to detect a situation where a new table
already exceeds the threshold.
No special event is triggered if a just resumed device's free space is below
the low water mark. However, resuming a device always triggers an
event; a userspace daemon should verify that free space exceeds the low
water mark when handling this event.
A low water mark for the metadata device is maintained in the kernel and
will trigger a dm event if free space on the metadata device drops below
......
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