[dm-devel] Re: dm snapshot: rework writing to snapshot origin
Mike Snitzer
snitzer at redhat.com
Tue Nov 17 17:49:03 UTC 2009
Alasdair,
I am not aware of any "cons" associated with this patch.
Mikulas are you? Alasdair would like both "pros" and "cons" documented
in the patch header.
Here is a revised patch header that now documents why this patch is a
prerequisite for snapshot-merge (specifically this patch:
http://patchwork.kernel.org/patch/60708/):
From: Mikulas Patocka <mpatocka at redhat.com>
The previous code selected one exception as "primary_pe", linked all
other exceptions on it and used reference counting to wait until all
exceptions are reallocated.
All the complexity with exceptions linking and reference counting has
been removed. Now, a bio is linked to one exception and when that
exception is reallocated, the bio is retried to possibly wait for other
exceptions.
The new __origin_write() interface affords the snapshot-merge support,
snapshot_merge_process() specifically, the ability to trigger exceptions
in other snapshots without having a need for an associated bio (which
snapshot-merge does not generate). As such this patch is a prerequisite
for snapshot-merge.
Signed-off-by: Mikulas Patocka <mpatocka at redhat.com>
Signed-off-by: Mike Snitzer <snitzer at redhat.com>
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