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Implement removal of files via blocks discarding according to configured bandwidth #2303

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Implement removal of files via blocks discarding according to configured bandwidth #2303

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Commits on Jun 27, 2024

  1. file_discard_queue: implement removal of files via blocks discarding 

    To avoid I/O latency spikes that are caused by too many TRIM requests
issued to the drive over a short period of time when the filesystem
is mounted with the online discard option and many files are removed,
the file_discard_queue class is used.

Instead of relying on the unlink operation that trims all extents of
a file at once, the approach that utilizes blocks discarding at a
given pace is used.

When a user wants to remove a file, then file_discard_queue::enqueue_file_removal()
needs to be called. Its main purpose is to store the information about the work
related to file discard in the internal data of the class.

Reactor will invoke file_discard_queue::try_discard_blocks() function via poller.
The function checks if the bandwidth of discards allows another block to be
discarded. If the bandwidth is available, then the discard is performed.

The described approach ensures, that the amount of removed data remains at
the configured level.

Signed-off-by: Patryk Wrobel <[email protected]>
    @pwrobelse
    pwrobelse committed Jun 27, 2024
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  2. file_discard_queue_test: implement basic unit tests 

    This patch introduces unit tests for file_discard_queue class.
To avoid interference between test cases, each of them manually
triggers file_discard_queue::try_discard_blocks().

In next patches file_discard_queue will be plugged into reactor
for each shard. Then another part of tests will be added as a
separate binary to check the full flow.

Signed-off-by: Patryk Wrobel <[email protected]>
    @pwrobelse
    pwrobelse committed Jun 27, 2024
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  3. reactor: allow users to discard files according to configured bandwidth 

    To enable usage of file_discard_queue in seastar applications,
it had to be plugged into reactor.

This patch introduces usage of file_discard_queue in reactor.
The following changes have been implemented:
 - remove_file_via_blocks_discarding() function is available
   and allows users to discard files according to a given
   bandwidth (using file_discard_queue)
 - file_discard_queue_submission_pollfn poller was added to
   reactor's main loop to trigger the work related to discarding
   files
 - I/O properties contain two new optional parameters:
   discard_block_size and discard_requests_per_second that
   allow a user to configure the bandwidth of discards for
   a given mountpoint

Signed-off-by: Patryk Wrobel <[email protected]>
    @pwrobelse
    pwrobelse committed Jun 27, 2024
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  4. file_discard_queue_global_test: implement tests for blocks discarding… 

    … removal

In order to ensure that file discard queue is
properly used by the reactor and can be configured
via I/O properties parameters a new set of global
tests was introduced.

To avoid any interferences between test cases, they
are run one after another in a seastar::thread.

The test cases verify the full flow including usage
of global utility functions, reactor, pollers and
configured file discard queues. The bandwidth of
discard operation is also verified.

Signed-off-by: Patryk Wrobel <[email protected]>
    @pwrobelse
    pwrobelse committed Jun 27, 2024
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