jbd2: add todo for a fast commit performance optimization
Fast commit performance can be optimized if commit thread doesn't wait for ongoing fast commits to complete until the transaction enters T_FLUSH state. Document this optimization. Suggested-by: Jan Kara <jack@suse.cz> Signed-off-by: Harshad Shirwadkar <harshadshirwadkar@gmail.com> Link: https://lore.kernel.org/r/20201106035911.1942128-11-harshadshirwadkar@gmail.com Signed-off-by: Theodore Ts'o <tytso@mit.edu>
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@ -450,6 +450,15 @@ void jbd2_journal_commit_transaction(journal_t *journal)
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schedule();
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write_lock(&journal->j_state_lock);
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finish_wait(&journal->j_fc_wait, &wait);
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/*
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* TODO: by blocking fast commits here, we are increasing
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* fsync() latency slightly. Strictly speaking, we don't need
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* to block fast commits until the transaction enters T_FLUSH
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* state. So an optimization is possible where we block new fast
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* commits here and wait for existing ones to complete
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* just before we enter T_FLUSH. That way, the existing fast
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* commits and this full commit can proceed parallely.
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*/
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}
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write_unlock(&journal->j_state_lock);
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