[dm-devel] [RFC] dm-raid1: not to add newly-allocated RH_CLEAN region to clean_regions

[Jun'ichi Nomura]

Hi,

I would like to know whether the attached patch is something
acceptable or not.

In dm-raid1.c, 'clean_regions' in region hash is a list used
to link regions which are clean AND no longer interested (freeable).
So I think it's safe not to add newly-allocated RH_CLEAN entry
to the list because someone who allocates it has interest
on the region.

In the current code, rh_alloc()/rh_find() is called from:
  - rh_inc(), which makes the state RH_DIRTY if it's RH_CLEAN
  - __rh_recovery_prepare(), which makes the state RH_RECOVERING
  - rh_delay(), which is called when the region is RH_RECOVERING

So none uses the newly allocated RH_CLEAN region as-is.
RH_DIRTY region is changed back to RH_CLEAN and then connected
to clean_regions when pending I/O completes.
RH_RECOVERING region is reclaimed when the recovery on the
region completes.

If this patch is acceptable, we can also merge RH_CLEAN and
RH_DIRTY into one state.

Comments are welcome.

Thanks,
Jun'ichi "Nick" Nomura
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