On 11/5/2018 10:58 AM, Adam Borowski wrote:
On Mon, Nov 05, 2018 at 08:31:46PM +0530, Pintu Agarwal wrote:
Hi,
I have one requirement: I wanted to have a swapfile (64MB to 256MB) on my system. But I wanted the data to be compressed and stored on the disk in my swapfile. [Similar to zram, but compressed data should be moved to disk, instead of RAM].
Note: I wanted to optimize RAM space, so performance is not important right now for our requirement.
So, what are the options available, to perform this in 4.x kernel version. My Kernel: 4.9.x Board: any - (arm64 mostly).
As I know, following are the choices: 1) ZRAM: But it compresses and store data in RAM itself 2) frontswap + zswap : Didn't explore much on this, not sure if this is helpful for our case. 3) Manually creating swapfile: but how to compress it ? 4) Any other options ?
Loop device on any filesystem that can compress (such as btrfs)? The performance would suck, though -- besides the indirection of loop, btrfs compresses in blocks of 128KB while swap wants 4KB writes. Other similar option is qemu-nbd -- it can use compressed disk images and expose them to a (local) nbd client.
Swap on any type of a networked storage device (NBD, iSCSI, ATAoE, etc) served from the local system is _really_ risky. The moment the local server process for the storage device gets forced out to swap, you deadlock. Performance isn't _too_ bad for the BTRFS case though (I've actually tested this before), just make sure you disable direct I/O mode on the loop device, otherwise you run the risk of data corruption.