Re: [PATCH v2 0/3] btrfs: Introduce new incompat feature BG_TREE to hugely reduce mount time

[Johannes Thumshirn <jthumshirn@suse.de>]

> [[Benchmark]]
> Since I have upgraded my rig to all NVME storage, there is no HDD
> test result.
> 
> Physical device:	NVMe SSD
> VM device:		VirtIO block device, backup by sparse file
> Nodesize:		4K  (to bump up tree height)
> Extent data size:	4M
> Fs size used:		1T
> 
> All file extents on disk is in 4M size, preallocated to reduce space usage
> (as the VM uses loopback block device backed by sparse file)

Do you have a some additional details about the test setup? I tried to
do the same (testing) for a bug Felix (added to Cc) reported to my at
the ALPSS Conference and I couldn't reproduce the issue.

My testing was a 100TB sparse file passed into a VM and running this
script to touch all blockgroups:

#!/bin/sh

FILE=/mnt/test

add_dirty_bg() {
        off="$1"
        len="$2"
        touch $FILE
        xfs_io -c "falloc $off $len" $FILE
        rm $FILE
}

mkfs.btrfs /dev/vda
mount /dev/vda /mnt

for ((i = 1; i < 100000; i++)); do
        add_dirty_bg $i"G" "1G"
done

umount /mnt



-- 
Johannes Thumshirn                            SUSE Labs Filesystems
jthumshirn@suse.de                                +49 911 74053 689
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