Question: background GC on UBIFS

[Wang Fangpeng]

Hi, folks,

We did some performance test of writing data to a ubifs volume by dd. The block
size of dd is 1MB.

When the volume has more than 20% free space, the speed of writing is about
1.4MB/s ~ 1.2MB/s.

However, when the free space is less and less, the speed decreases to about
83KB/s. We think the overhead is caused by GC, since GC tries to find a free
space and move valid data to another place to get a free block.

Although we already have a kthread to collect freeable blocks, it doesn't
touch blocks which have both valid and invalid nodes. My question is why don't
we do such consolidation/defragmentation periodicly, so that the overhead
could be decreased when there is not enough free space?

thanks.