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Rather than always releasing the prisoners in a cell, the client may
want to promote one of them to be the new holder. There is a race here
though between releasing an empty cell, and other threads adding new
inmates. So this function makes the decision with its lock held.
This function can have two outcomes:
i) An inmate is promoted to be the holder of the cell (return value of 0).
ii) The cell has no inmate for promotion and is released (return value of 1).
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
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Ranges will be placed in the same cell if they overlap.
Range locking is a prerequisite for more efficient multi-block discard
support in both the cache and thin-provisioning targets.
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
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This use of direct submission in process_prepared_mapping() reduces
latency for submitting bios in a cell by avoiding adding those bios to
the deferred list and waiting for the next iteration of the worker.
But this direct submission exposes the potential for a race between
releasing a cell and incrementing deferred set. Fix this by introducing
dm_cell_visit_release() and refactoring inc_remap_and_issue_cell()
accordingly.
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
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This avoids dropping the cell, so increases the probability that other
bios will collect within the cell, rather than being passed individually
to the worker.
Also add required process_cell and process_discard_cell error handling
wrappers and set associated pool-mode function pointers accordingly.
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
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Previously it was using a fixed sized hash table. There are times
when very many concurrent cells are held (such as when processing a very
large discard). When this happens the hash table performance becomes
very poor.
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
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Update the DM thin provisioning target's allocation failure error to be
consistent with commit a9d6ceb8 ("[SCSI] return ENOSPC on thin
provisioning failure").
The DM thin target now returns -ENOSPC rather than -EIO when
block allocation fails due to the pool being out of data space (and
the 'error_if_no_space' thin-pool feature is enabled).
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Acked-By: Joe Thornber <ejt@redhat.com>
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Add a target that allows a fast device such as an SSD to be used as a
cache for a slower device such as a disk.
A plug-in architecture was chosen so that the decisions about which data
to migrate and when are delegated to interchangeable tunable policy
modules. The first general purpose module we have developed, called
"mq" (multiqueue), follows in the next patch. Other modules are
under development.
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Heinz Mauelshagen <mauelshagen@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
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This patch takes advantage of the new bio-prison interface where the
memory is now passed in rather than using a mempool in bio-prison.
This allows the map function to avoid performing potentially-blocking
allocations that could lead to deadlocks: We want to avoid the cell
allocation that is done in bio_detain.
(The potential for mempool deadlocks still remains in other functions
that use bio_detain.)
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
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Change the dm_bio_prison interface so that instead of allocating memory
internally, dm_bio_detain is supplied with a pre-allocated cell each
time it is called.
This enables a subsequent patch to move the allocation of the struct
dm_bio_prison_cell outside the thin target's mapping function so it can
no longer block there.
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
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Change existing users of the function dm_cell_release_singleton to share
cell_defer_except instead, and then remove the now-unused function.
Everywhere that calls dm_cell_release_singleton, the bio in question
is the holder of the cell.
If there are no non-holder entries in the cell then cell_defer_except
behaves exactly like dm_cell_release_singleton. Conversely, if there
*are* non-holder entries then dm_cell_release_singleton must not be used
because those entries would need to be deferred.
Consequently, it is safe to replace use of dm_cell_release_singleton
with cell_defer_except.
This patch is a pre-requisite for "dm thin: fix race between
simultaneous io and discards to same block".
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
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The bio prison code will be useful to other future DM targets so
move it to a separate module.
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
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