On 05/30/2020 12:13 PM, Pavel Machek wrote:
Hi!
For example, you can use proxy device to store hot data only. With
such strategy new logical blocks (which are always "cold") will always
go to the main storage (in contrast with Burst Buffers, where new
logical blocks first get written to the proxy disk). Once in a while
you need to scan your volume in order to push colder data out, and
pull hotter data in the proxy disk. Reiser5 contains a common
interface for this. It is possible to maintain per-file, or even per-
blocks-extent "temperature" of data (e.g. as a generation counter),
Would it be possible to offer userland interface for this? I can
probably say that mp3/video files should be cold, while some source
files should be hot, etc...
Best regards,
Pavel
Hi Pavel,
Yes, it is possible. One just needs to add an ioctl handler for regular
files managed by a plugin with STRIPED_FILE_PLUGIN_ID. That handler is
to set user-defined "temperature" to a file.
Also we'll need an additional on-disk file attribute (32 (or 64?)-bit
field in the private part of inode) to store the "temperature" in. It
can be added by standard way via implementation of respective stat-data
extension in the file reiser4/plugin/item/static_stat.c
Finally, we'll need to handle temperature in the common migration
procedure balance_volume_asym(), which is responsible for clearing up
the proxy device. It should look like this:
...
if (!IS_ERR(inode) && inode_file_plugin(inode)->balance &&
file_is_cold_enough(inode)) {
reiser4_iget_complete(inode);
/*
* migrate data blocks of this file
*/
...
Currently it works as if all files are "cold" (i.e. migrates
everything).
Once I find the current stuff more-or-less stable I'll add temperature
support and send the patch.
Thanks,
Edward.
