Btrfs: avoid unnecessary ordered extent cache resets
After an ordered extent completes, don't blindly reset the inode's ordered tree last accessed ordered extent pointer. While running the xfstests I noticed that about 29% of the time the ordered extent to which tree->last pointed was not the same as our just completed ordered extent. After that I ran the following sysbench test (after a prepare phase) and noticed that about 68% of the time tree->last pointed to a different ordered extent too. sysbench --test=fileio --file-num=32 --file-total-size=4G \ --file-test-mode=rndwr --num-threads=512 \ --file-block-size=32768 --max-time=60 --max-requests=0 run Therefore reset tree->last on ordered extent removal only if it pointed to the ordered extent we're removing from the tree. Results from 4 runs of the following test before and after applying this patch: $ sysbench --test=fileio --file-num=32 --file-total-size=4G \ --file-test-mode=seqwr --num-threads=512 \ --file-block-size=32768 --max-time=60 --file-io-mode=sync prepare $ sysbench --test=fileio --file-num=32 --file-total-size=4G \ --file-test-mode=seqwr --num-threads=512 \ --file-block-size=32768 --max-time=60 --file-io-mode=sync run Before this path: run 1 - 64.049Mb/sec run 2 - 63.455Mb/sec run 3 - 64.656Mb/sec run 4 - 63.833Mb/sec After this patch: run 1 - 66.149Mb/sec run 2 - 68.459Mb/sec run 3 - 66.338Mb/sec run 4 - 66.176Mb/sec With random writes (--file-test-mode=rndwr) I had huge fluctuations on the results (+- 35% easily). Signed-off-by: Filipe David Borba Manana <fdmanana@gmail.com> Signed-off-by: Josef Bacik <jbacik@fb.com> Signed-off-by: Chris Mason <clm@fb.com>
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@ -520,7 +520,8 @@ void btrfs_remove_ordered_extent(struct inode *inode,
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spin_lock_irq(&tree->lock);
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node = &entry->rb_node;
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rb_erase(node, &tree->tree);
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tree->last = NULL;
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if (tree->last == node)
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tree->last = NULL;
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set_bit(BTRFS_ORDERED_COMPLETE, &entry->flags);
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spin_unlock_irq(&tree->lock);
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