Google Continues Working On Suspend-Only Swap Spaces For Linux
Written by Michael Larabel in Linux Kernel on 26 July 2021 at 08:30 PM EDT. 48 Comments
LINUX KERNEL --
Google engineers and other parties are interested in being able to create swap spaces on Linux systems that would be reserved just for system suspend/hibernation purposes and not for generic swapping to disk.

The proposed SWAP_FLAG_HIBERNATE_ONLY would reserve a swap space just for suspend-to-disk usage and not swapping regular pages. To now, generic swap ultimately needs to be enabled if just wanting to use it for system suspend, short of workarounds for turning it on/off around the suspend process.

Among the motives for suspend-only swap spaces:
There are a few reasons why usermode might want to be able to exclusively steer swap and hibernate. One reason relates to SSD wearing. Hibernate's endurance and speed requirements are different from swap. It may for instance be advantageous to keep hibernate in primary storage, but put swap in an SLC namespace. These namespaces are faster and have better endurance, but cost 3-4x in terms of capacity. Exclusively steering hibernate and swap enables system designers to accurately partition their storage without either wearing out their primary storage, or overprovisioning their fast swap area.

Another reason to allow exclusive steering has to do with security. The requirements for designing systems with resilience against offline attacks are different between swap and hibernate. Swap effectively requires a dictionary of hashes, as pages can be added and removed arbitrarily, whereas hibernate only needs a single hash for the entire image. If you've set up block-level integrity for swap and image-level integrity for hibernate, then allowing swap blocks to possibly leak out to the hibernate region is problematic, since it creates swap pages not protected by any integrity.

Sent out today was the latest patch implementing this hibernate-only flag for swap. This revision changes the flag name and has various other code improvements for this proposed functionality.
Related News
About The Author
Author picture

Michael Larabel is the principal author of Phoronix.com and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 20,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated benchmarking software. He can be followed via Twitter or contacted via MichaelLarabel.com.

Popular News This Week