generic zswap dedup
a project by ailiopoulos
Updated about 3 years ago. 4 hacker ♥️. 1 follower.

Project Description

zswap [1] is a linux kernel component that provides in-memory compression for swap pages. It already provides a limited form of deduplication: if a page is filled with the same value (e.g. all-zeroes) then only that value is kept instead of compressing the contents.

This project proposes to enhance zswap with a more general and powerful dedup capability: pages that contain the same content (as identified by a checksum or hash value across the entire page contents) will be stored only once in the compressed pool.

This would be somewhat similar in spirit to what ksm [2] does, that is consolidation of identical pages of anonymous memory. There are some differences though, primarily ksm requires userspace to explicitly opt-in (via madvise/MADV_MERGEABLE) and operates on active pages that have not been selected for eviction from memory. On the other hand zswap operates transparently from the applications (it applies to all pages of anonymous memory that are on their way to swap).

Goal for this Hackweek

Have a first working POC.

Resources

  • [1] https://www.kernel.org/doc/html/latest/admin-guide/mm/zswap.html
  • [2] https://www.kernel.org/doc/html/latest/admin-guide/mm/ksm.html

Join this project

Looking for hackers with the skills:

kernel

This project is part of:

Hack Week 21

Activity

  • about 3 years ago: ailiopoulos liked this project.
  • about 3 years ago: dmdiss liked this project.
  • about 3 years ago: shunghsiyu liked this project.
  • about 3 years ago: ailiopoulos added keyword "kernel" to this project.
  • about 3 years ago: mbrugger liked this project.
  • about 3 years ago: ailiopoulos started this project.
  • about 3 years ago: ailiopoulos originated this project.


    • Comments

    Be the first to comment!

    Similar Projects

    early stage kdump support by mbrugger

    Project Description

    When we experience a early boot crash, we are not able to analyze the kernel dump, as user-space wasn't able to load the crash system. The idea is to make the crash system compiled into the host kernel (think of initramfs) so that we can create a kernel dump really early in the boot process.

    Goal for the Hackweeks

    1. Investigate if this is possible and the implications it would have (done in HW21)
    2. Hack up a PoC (done in HW22 and HW23)
    3. Prepare RFC series (giving it's only one week, we are entering wishful thinking territory here).

    update HW23

    • I was able to include the crash kernel into the kernel Image.
    • I'll need to find a way to load that from init/main.c:start_kernel() probably after kcsan_init()
    • I workaround for a smoke test was to hack kexec_file_load() systemcall which has two problems:
      1. My initramfs in the porduction kernel does not have a new enough kexec version, that's not a blocker but where the week ended
      2. As the crash kernel is part of init.data it will be already stale once I can call kexec_file_load() from user-space.

    The solution is probably to rewrite the POC so that the invocation can be done from init.text (that's my theory) but I'm not sure if I can reuse the kexec infrastructure in the kernel from there, which I rely on heavily.

    update HW24

    • Day1
      • rebased on v6.12 with no problems others then me breaking the config
      • setting up a new compilation and qemu/virtme env
      • getting desperate as nothing works that used to work
    • Day 2
      • getting to call the invocation of loading the early kernel from __init after kcsan_init()

    • Day 3

      • fix problem of memdup not being able to alloc so much memory... use 64K page sizes for now
      • code refactoring
      • I'm now able to load the crash kernel
      • When using virtme I can boot into the crash kernel, also it doesn't boot completely (major milestone!), crash in elfcorehdr_read_notes()

    • Day 4

      • crash systems crashes (no pun intended) in copy_old_mempage() link; will need to understand elfcorehdr...
      • call path vmcore_init() -> parse_crash_elf_headers() -> elfcorehdr_read() -> read_from_oldmem() -> copy_oldmem_page() -> copy_to_iter()

    • Day 5

      • hacking arch/arm64/kernel/crash_dump.c:copy_old_mempage() to see if crash system really starts. It does.
      • fun fact: retested with more reserved memory and with UEFI FW, host kernel crashes in init but directly starts the crash kernel, so it works (somehow) \o/

    • TODOs

      • fix elfcorehdr so that we actually can make use of all this...
      • test where in the boot __init() chain we can/should call kexec_early_dump()