linux-kernel - Re: Creating compressed backing

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Message-ID: <20181105155815.i654i5ctmfpqhggj@angband.pl>
Date:   Mon, 5 Nov 2018 16:58:15 +0100
From:   Adam Borowski <kilobyte@...band.pl>
To:     Pintu Agarwal <pintu.ping@...il.com>
Cc:     linux-mm@...ck.org, open list <linux-kernel@...r.kernel.org>,
        kernelnewbies@...nelnewbies.org
Subject: Re: Creating compressed backing_store as swapfile

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.


Meow!
-- 
⢀⣴⠾⠻⢶⣦⠀ Have you heard of the Amber Road?  For thousands of years, the
⣾⠁⢰⠒⠀⣿⡁ Romans and co valued amber, hauled through the Europe over the
⢿⡄⠘⠷⠚⠋⠀ mountains and along the Vistula, from Gdańsk.  To where it came
⠈⠳⣄⠀⠀⠀⠀ together with silk (judging by today's amber stalls).