Quickstart guide and broken link to full documentation

[TheLinuxGuy]

Hi, pcache looks very promising and I look forward to testing it soon. In the meantime, I wanted to share some feedback and ideas.

1. Current README.md file has a broken link - 404 to https://datatravelguide.github.io/dtg-blog/pcache/pcache.html

2. Would you consider including a quickstart examples on how to setup and manage pcache? For example; it seems that pcache is designed to NOT require me to reformat any disks (e.g: slow hdds) if all I wish to do is put my nvme disk as cache layer to speed up I/O.

3. Since pcache is being advertised as better than bcache, could as part of the utils package include some kind of stats option? an idea you could copy: https://gist.github.com/damoxc/6267899

[yangdongsheng]

@TheLinuxGuy Thanx for your information, but I have to say the pcache-utils is not used for pcache anymore.

When I develope RFC for pcache, I define pcache as an single block device but that introduce new userspace tools like pcache-utils. It increase the overhead of distro and there is an existing path to do it: device mapper.

So the current sutatus of pcache is dm-pcache in device mapper subdir. and it was queued in dm-6.18, so it will be mainline in next merge window if all things are going well.

You can pull the dm-6.18 from kernel.org: https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/log/?h=dm-6.18

and there is a document in Documentation/admin-guide/device-mapper/dm-pcache.rst .

`

1. Create devices

dmsetup create pcache_sdb --table
"0 $(blockdev --getsz /dev/sdb) pcache /dev/pmem0 /dev/sdb 4 cache_mode writeback data_crc true"

2. Put a filesystem on top

mkfs.ext4 /dev/mapper/pcache_sdb
mount /dev/mapper/pcache_sdb /mnt

3. Tune GC threshold to 80 %

dmsetup message pcache_sdb 0 gc_percent 80

4. Observe status

watch -n1 'dmsetup status pcache_sdb'

5. Shutdown

umount /mnt
dmsetup remove pcache_sdb
`
An example in that document, you dont need to install application for pcache, just dmsetup can do the all thing.

At last, I would say, current pcache is working on pmem as the cache_dev, if you want to use it on nvme, you can send your requirement in linux-dm maillist, I will see how many people want this feature.

Thanx

[TheLinuxGuy]

ok thank you will look into it.

Is the mailing list you suggest i propose nvme this one https://lore.kernel.org/dm-devel/

[yangdongsheng]

ok thank you will look into it.

Is the mailing list you suggest i propose nvme this one https://lore.kernel.org/dm-devel/

Yes, this is correct mailist :)