Swapfiles by default in Ubuntu

4MB RAM card

By default, in Ubuntu, we usually create a swap partition.

Back in the day of 4MB RAM cards this made total sense, as the ration of RAM to disk space, was still very low. Things have changed since. Server, desktop, embedded systems have migrated to newer generations of both RAM and persistent storage. On the high performance side of things we see machines with faster storage in the form of NVMe and SSD drives. Reserving space for swap on such storage, can be seen as expensive and wasteful. This is also true for recent enough laptops and desktops too. Mobile phones have substantial amounts of RAM these days, and at times, coupled with eMMC storage - it is flash storage of lower performance, which have limited number of write cycles, hence should not be overused for volatile swap data. And there are also unicorns in a form of high performance computing of high memory (shared memory) systems with little or no disk space.

Today, carving a partition and reserving twice the RAM size for swap makes little sense. For a common, general, machine most of the time this swap will not be used at all. Or if said swap space is in use but is of inappropriate size, changing it in-place in retrospect is painful.

Starting from 17.04 Zesty Zapus release, instead of creating swap partitions, swapfiles will be used by default for non-lvm based installations.

Secondly, the sizing of swapfiles is very different. It is no more than 5% of free disk space or 2GiB, whichever is lower.

For preseeding, there are two toggles that control this behavior:

d-i partman-swapfile/percentage string 5
d-i partman-swapfile/size string 2048

Setting either of those to zero, will result in system without any swap at all. And one can tweak relative integer percentage points and absolute limits in integer percentage points or MiB.

On LVM based installations, swap logical volumes are used, since unfortunately LVM snapshots do not exclude swapfile changes. However, I would like to move partman-auto to respect the above proposed 5%-or-2GB limits.

Ps. 4MB RAM card picture is by Bub's (Photo) [GFDL or CC-BY-SA-3.0], via Wikimedia Commons

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