Re: [PATCH md-6.13] md: remove bitmap file support

[Dragan Milivojević]

On Fri, 8 Nov 2024 at 07:07, Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> wrote:


> I don't think external bitmap can workaround the performance degradation
> problem, because the global lock for the bitmap are the one to blame for
> this, it's the same for external or internal bitmap.

Not according to my tests:

5 disk RAID5, 64K chunk



Test                   BW         IOPS
bitmap internal 64M    700KiB/s   174
bitmap internal 128M   702KiB/s   175
bitmap internal 512M   1142KiB/s  285
bitmap internal 1024M  40.4MiB/s  10.3k
bitmap internal 2G     66.5MiB/s  17.0k
bitmap external 64M    67.8MiB/s  17.3k
bitmap external 1024M  76.5MiB/s  19.6k
bitmap none            80.6MiB/s  20.6k
Single disk 1K         54.1MiB/s  55.4k
Single disk 4K         269MiB/s   68.8k



Full test logs with system details at: pastebin. com/raw/TK4vWjQu


>
> Do you know that is there anyone using external bitmap in the real
> world? And is there numbers for performance? We'll have to consider
> to keep it untill the new lockless bitmap is ready if so.

Well I am and it's a royal pain but there isn't much of an alternative.