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android / platform / system / memory / mmd / f653063
commitf653063701f443515331837a6f4a3807e90b4ba6[log] [tgz]
authorCharisee <chiw@google.com>Wed Jul 09 22:51:25 2025 +0000
committerCharisee Chiw <chiw@google.com>Wed Jul 09 18:44:13 2025 -0700
tree050e95f5265578b5fda0665697716a87e87f8c2d
parent4e1eb17489f4deaa375c5551100401d69310ff56 [diff]
Fixes for Rust v1.85.1

Bug: http://b/421269002
Test: m rust
Change-Id: I113c54e7d069cbffd864a1f8eb107a7b7e14c69b
2 files changed
tree: 050e95f5265578b5fda0665697716a87e87f8c2d
  1. aidl/
  2. api/
  3. src/
  4. .clang-format ⇨ ../../../build/soong/scripts/system-clang-format
  5. .gitignore
  6. Android.bp
  7. flags.aconfig
  8. mmd.rc
  9. MmdProperties.sysprop
  10. OWNERS
  11. PREUPLOAD.cfg
  12. README.md
  13. rustfmt.toml
  14. TEST_MAPPING
README.md

Android Memory Management Daemon

Overview

The Android Memory Management Daemon (mmd) is a new native daemon designed to handle Android memory management configuration and tunables.

Background

Before mmd, Android ZRAM configurations were fragmented and offered limited customization. mmd addresses this by centralizing ZRAM management, enabling more complex configuration logic. This unified approach simplifies adding new features and improvements to ZRAM management. Another motivation for mmd is a separation of concerns between system server and swap management.

ZRAM management

On boot complete, mmd will try to set up ZRAM with specified configuration. Once the ZRAM setup is done, mmd service is enabled to handle ZRAM maintenance tasks.

With mmd ZRAM setup, ZRAM maintenance is initiated from system server by sending Binder requests to mmd via the IMmd interface. mmd handles the actual maintenance tasks of doing ZRAM writeback and recompression based on its own policy. Both the scheduling from system server and the ZRAM maintenance policies can be configured via system properties as mentioned in the ZRAM maintenance section.

ZRAM setup configuration

mmd ZRAM setup can be configured using following system properties:

  • mmd.zram.enabled: whether mmd ZRAM setup is enabled. Default = false.
  • mmd.zram.comp_algorithm: ZRAM compression algorithm. Kernel default compression algorithm will be used if not specified[^zram-comp-algo].
  • mmd.zram.size: ZRAM device size in bytes, or a percentage of device RAM size (eg: 75%). Default = 50%.
  • mmd.zram.writeback.enabled: whether to enable ZRAM writeback. Default = false.
  • mmd.zram.writeback.device_size: the size of the writeback device in bytes or percentage of the data partition. The actual device size can be adjusted based on available space of the data partition. Default = 1073741824 (1 GiB).
  • mmd.zram.writeback.min_free_space_mib: minimum free space in MiB that needs to be available after the writeback device is set up. Default = 1536 (1.5 GiB).
  • mmd.zram.recompression.enabled: whether to enable ZRAM recompression feature. Default = false.
  • mmd.zram.recompression.algorithm: ZRAM recompression algorithm. Default = zstd[^zram-comp-algo].

ZRAM maintenance configuration

ZRAM maintenance should work out of the box, but it can be finetuned further using below system properties:

ZRAM maintenance scheduling:

  • mm.zram.maintenance.first_delay_seconds: the delay before the first ZRAM maintenance is initiated. Default = 3600 (1 hour).
  • mm.zram.maintenance.periodic_delay_seconds: the delay between subsequent ZRAM maintenance scheduling. Default = 3600 (1 hour).
  • mm.zram.maintenance.idle_only: whether to only initiate ZRAM maintenance when the device is idle. Default = true.
  • mm.zram.maintenance.require_battery_not_low: whether to require battery not low before initiating ZRAM maintenance. Default = true.

mmd ZRAM writeback policy:

  • mmd.zram.writeback.backoff_seconds: the backoff time since the last writeback. Default = 600 (10 minutes).
  • mmd.zram.writeback.idle_min_seconds: minimum seconds to be used for calculating idle page age dynamically based on memory utilization. A fixed idle age will be used when this is the same as idle_max_seconds system property. Default = 72000 (20 hours).
  • mmd.zram.writeback.idle_max_seconds: maximum seconds to be used for calculating idle page age dynamically based on memory utilization. A fixed idle age will be used when this is the same as idle_min_seconds system property. Default = 90000 (25 hours).
  • mmd.zram.writeback.huge_enabled: whether to enable HUGE page writeback. Default = false.
  • mmd.zram.writeback.idle_enabled: whether to enable IDLE page writeback. Default = true.
  • mmd.zram.writeback.huge_idle_enabled: whether to enable HUGE_IDLE page writeback. Default = true.
  • mmd.zram.writeback.min_bytes: minimum bytes to write back in 1 round. Default = 5242880 (5 MiB).
  • mmd.zram.writeback.max_bytes: maximum bytes to write back in 1 round. Default = 314572800 (300 MiB).
  • mmd.zram.writeback.max_bytes_per_day: maximum bytes to write back in 1 day. Default = 1073741824 (1 GiB).
  • mmd.zram.writeback.limit.enabled: whether to enable the ZRAM writeback limit. Default = true.

mmd ZRAM recompression policy:

  • mmd.zram.recompression.backoff_seconds: the backoff time since the last recompression. Default = 1800 (30 minutes).
  • mmd.zram.recompression.min_idle_seconds: minimum seconds to be used for calculating idle page age dynamically based on memory utilization. A fixed idle age will be used when this is the same as idle_max_seconds system property. Default = 7200 (2 hours).
  • mmd.zram.recompression.max_idle_seconds: maximum seconds to be used for calculating idle page age dynamically based on memory utilization. A fixed idle age will be used when this is the same as idle_min_seconds system property. Default = 14400 (4 hours).
  • mmd.zram.recompression.threshold_bytes: the minimum size in bytes of ZRAM pages to be considered for recompression. Default = 1024 (1 KiB).
  • mmd.zram.recompression.huge_enabled: whether to enable HUGE page recompression. Default = true.
  • mmd.zram.recompression.idle_enabled:whether to enable IDLE page recompression. Default =true`.
  • mmd.zram.recompression.huge_idle_enabled: whether to enable HUGE_IDLE page recompression. Default = true.

Zram idle pages tracking

mmd ZRAM maintenance marks ZRAM pages as idle based on how long it has been since they were last accessed. This feature requires the CONFIG_ZRAM_TRACK_ENTRY_ACTIME or CONFIG_ZRAM_MEMORY_TRACKING kernel configs to be enabled.

If the kernel config is not enabled, mmd ZRAM maintenance falls back to a substitute logic to get idle zram pages.

  1. Mark all zram pages as idle when mmd starts.
  2. Skip next zram maintenances until required idle duration has passed.
  3. Zram writeback/recompress idle pages. If there are remaining idle pages due to writeback limit, mmd continues to writeback pages on the next zram maintenance without marking pages as idle (i.e. without moving to step 4).
  4. If all idle pages are written back, mark all zram pages as idle again and move back to the step 2. If zram writeback is disabled, mmd marks all zram pages as idle when zram recompression happens after the idle duration of recompression.

Note that idle duration of zram writeback and recompression is usually different and recompression is shorter. Some zram maintenances can just recompress idle pages and skip writeback until writeback idle duration has passed at the step 3.

Caveats

mmd ZRAM maintenance is only guaranteed to work with the ZRAM device set up by mmd --setup-zram.

Existing ZRAM setup deprecation

While swapon_all is still available to set up ZRAM and disk-based swap space, mmd is the preferred approach for ZRAM management for easier configuration and additional features like ZRAM recompression.

When mmd ZRAM setup is enabled via mmd.zram.enabled system property:

  • ZRAM setup in swapon_all implementation is a no-op.
  • Existing ZRAM configuration such as config_zramWriteback feature in the overlay config.xml file, and ro.zram.* writeback system properties are ignored.

Development guide

Apply rustfmt

Before upload your changes, please apply rustfmt.

rustfmt +nightly **/*.rs

[^zram-comp-algo] cat /sys/block/zram0/comp_algorithm gives the available compression algorithms (as well as the current one included in brackets).