Difference between ZRAM and ZSWAP

Question

zram

Status: Available in mainline kernel as of version 3.14 (March 2014)
Implementation: compressed block device, memory is dynamically
allocated as data is stored
Usage: Configure zram block device as a swap device to eliminate need
for physical swap defice or swap file
Benefits:
1. Eliminates need for physical swap device. This beame popular when
  netbooks first showed up. Zram (then compcache) allowed users to
  avoid swap shortening the lifespan of SSDs in these memory
  constrained systems.
2. A zram block device can be used for other applications other than
  swap, anything you might use a block device for conceivably.
Drawbacks:
1. Once a page is stored in zram it will remain there until paged in or
  invalidated. The first pages to be paged out will be the oldest
  pages (LRU list), these are ‘cold’ pages that are infrequently
  access. As the system continues to swap it will move on to pages
  that are warmer (more frequently accessed), these may not be able to
  be stored because of the swap slots consumed by the cold pages. What
  zram can not do (compcache had the option to configure a block
  backing device) is to evict pages out to physical disk. Ideally you
  want to age data out of the in-kernel compressed swap space out to
  disk so that you can use kernel memory for caching warm swap pages
  or free it for more productive use.

Status: Available in mainline kernel as of version 3.11 (September 2013)
Implementation: compressed in-kernel cache for swap pages. In-kernel
cache is compressed, the compression algorithm is pluggable using the
CryptoAPI and the storage for pages is dynamically allocated. Older
pages can be evicted to disk making this a sort of write-behind
cache.
Usage: Cache swap pages destined for regular swap devices (or swap
files).
Benefits:
1. Integration with swap code (using Frontswap API) allows zswap to
  choose to store only pages that compress well and handle memory
  allocation failures, in those cases pages are sent to the backing
  swap device.
2. Oldest pages in the cache are pushed out to backing swap device to
  make room for newer pages, this solves the LRU inversion problem
  that a lack of page eviction would present.
Drawbacks:
1. Needs a physical swap device (or swapfile).