What is an alternative for zcache?
Indeed zcache appears to have been discontinued, as it was removed from kernel 3.11 for being effectively obsolete. The commit message of zcache removal reads
staging: zcache: delete it
zcache is obsolete and not used anymore, Bob Liu has rewritten it and is submitting it for inclusion through the main -mm tree, as it should have been done in the first place...
It appears that Bob Liu's submission never got into mainline.
Now, the way I understand it, the page cache is automatically "dropped" (cleared) in an out-of-memory scenario. zcache actually implemented compression so it could maintain more filesystem pages (also known as "vfs cache" or "inode/dentry cache") before being dropped.
The Linux kernel has zswap today that implements compressed disk-based swapping, but doesn't compress filesystem pages.
I am not aware of a current day alternative for zcache.
Perhaps as a workaround, if you are concerned with performance degradation due to filesystem pages being freed, consider tuning vm.vfs_cache_pressure as instructed here.
For normal workloads it's safe to just settle with zswap.
Additional reading:
- zram vs zswap vs zcache Ultimate guide: when to use which one
- Zswap, Zram, Zcache desktop usage scenarios
- zswap (Arch Linux Wiki)
- Cleancache and Frontswap (LWN)
- The Case for Compressed Caching in Virtual Memory Systems