dm cache: submit writethrough writes in parallel to origin and cache

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Discontinue issuing writethrough write IO in series to the origin and
then cache.

Use bio_clone_fast() to create a new origin clone bio that will be
mapped to the origin device and then bio_chain() it to the bio that gets
remapped to the cache device.  The origin clone bio does _not_ have a
copy of the per_bio_data -- as such check_if_tick_bio_needed() will not
be called.

The cache bio (parent bio) will not complete until the origin bio has
completed -- this fulfills bio_clone_fast()'s requirements as well as
the requirement to not complete the original IO until the write IO has
completed to both the origin and cache device.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>

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This commit is contained in:

Mike Snitzer 2017-10-19 17:16:54 -04:00

parent 8e3c382777

commit 2df3bae9a6

1 changed files with 37 additions and 17 deletions

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54

drivers/md/dm-cache-target.c

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