[linux-lvm] 2 questions on LVM cache

[linux-lvm] 2 questions on LVM cache

[Xen]

1. Does LVM cache support discards of the underlying blocks (in the 
cache) when the filesystem discards the blocks?

I was reading https://lwn.net/Articles/293658/ which makes it clear that 
years ago kernel developers were introducing discard behaviour into 
Linux filesystems with respect to flash devices and their need to copy 
for wear leveling.

I know so little about it, but I have seen the "discard" flag mentioned 
so much with respect to SSDs, that I must assume these discards are 
there. Are LVM cache blocks discarded when the filesystem layer discards 
these blocks?

Where can I find this info?

In https://www.redhat.com/archives/linux-lvm/2016-April/msg00030.html I 
mentioned that such a discard feature would be necessary in order for a 
filesystem to communicate to a block device layer which blocks are in 
use, and for a block device layer to communicate back a set of available 
blocks if these dynamically change.




I forgot the other question lol.

I'm interested in this solution to 
"https://bugzilla.redhat.com/show_bug.cgi?id=1189215" but I will respond 
in my other email (LVM Thin: Handle out of space conditions better).

Re: [linux-lvm] 2 questions on LVM cache

[Zdenek Kabelac]

On 27.4.2016 12:50, Xen wrote:
> 1. Does LVM cache support discards of the underlying blocks (in the cache)
> when the filesystem discards the blocks?

It does in a devel branch - hopefully will be upstreamed shortly...

Regards

Zdenek