Use default without sparse files, and add support to ext4 and xfs

Author: bigbruno

.gitignore

@@ -1,3 +1,169 @@
-systemd-swap[_-]*
-swap.conf
-*.new
+# Byte-compiled / optimized / DLL files
+__pycache__/
+*.py[cod]
+*$py.class
+
+# C extensions
+*.so
+
+# Distribution / packaging
+.Python
+build/
+develop-eggs/
+dist/
+eggs/
+.eggs/
+parts/
+sdist/
+wheels/
+share/python-wheels/
+*.egg-info/
+.installed.cfg
+*.egg
+MANIFEST
+result
+
+feedback.md
+VTE-llms.txt
+
+# PyInstaller
+#  Usually these files are written by a python script from a template
+#  before PyInstaller builds the exe, so as to inject date/other infos into it.
+*.manifest
+*.spec
+
+# Installer logs
+pip-log.txt
+pip-delete-this-directory.txt
+
+# Unit test / coverage reports
+htmlcov/
+.tox/
+.nox/
+.coverage
+.coverage.*
+.cache
+nosetests.xml
+coverage.xml
+*.cover
+*.py,cover
+.hypothesis/
+.pytest_cache/
+cover/
+
+# Django stuff:
+*.log
+local_settings.py
+db.sqlite3
+db.sqlite3-journal
+
+# Flask stuff:
+instance/
+.webassets-cache
+
+# Scrapy stuff:
+.scrapy
+
+# PyBuilder
+.pybuilder/
+target/
+
+# Jupyter Notebook
+.ipynb_checkpoints
+
+# IPython
+profile_default/
+ipython_config.py
+
+# pyenv
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+#   intended to run in multiple environments; otherwise, check them in:
+# .python-version
+
+# pipenv
+#   According to pypa/pipenv#598, it is recommended to include Pipfile.lock in version control.
+#   However, in case of collaboration, if having platform-specific dependencies or dependencies
+#   having no cross-platform support, pipenv may install dependencies that don't work, or not
+#   install all needed dependencies.
+#Pipfile.lock
+
+# UV
+#   Similar to Pipfile.lock, it is generally recommended to include uv.lock in version control.
+#   This is especially recommended for binary packages to ensure reproducibility, and is more
+#   commonly ignored for libraries.
+#uv.lock
+
+# poetry
+#   Similar to Pipfile.lock, it is generally recommended to include poetry.lock in version control.
+#   This is especially recommended for binary packages to ensure reproducibility, and is more
+#   commonly ignored for libraries.
+#   https://python-poetry.org/docs/basic-usage/#commit-your-poetrylock-file-to-version-control
+#poetry.lock
+
+# pdm
+#   Similar to Pipfile.lock, it is generally recommended to include pdm.lock in version control.
+#pdm.lock
+#   pdm stores project-wide configurations in .pdm.toml, but it is recommended to not include it
+#   in version control.
+#   https://pdm.fming.dev/latest/usage/project/#working-with-version-control
+.pdm.toml
+.pdm-python
+.pdm-build/
+
+# PEP 582; used by e.g. github.com/David-OConnor/pyflow and github.com/pdm-project/pdm
+__pypackages__/
+
+# Celery stuff
+celerybeat-schedule
+celerybeat.pid
+
+# SageMath parsed files
+*.sage.py
+
+# Environments
+.env
+.venv
+env/
+venv/
+ENV/
+env.bak/
+venv.bak/
+.direnv/
+.serena
+
+# Spyder project settings
+.spyderproject
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+
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+.ropeproject
+
+# mkdocs documentation
+/site
+
+# mypy
+.mypy_cache/
+.dmypy.json
+dmypy.json
+
+# Pyre type checker
+.pyre/
+
+# pytype static type analyzer
+.pytype/
+
+# Cython debug symbols
+cython_debug/
+
+# PyCharm
+#  JetBrains specific template is maintained in a separate JetBrains.gitignore that can
+#  be found at https://github.com/github/gitignore/blob/main/Global/JetBrains.gitignore
+#  and can be added to the global gitignore or merged into this file.  For a more nuclear
+#  option (not recommended) you can uncomment the following to ignore the entire idea folder.
+#.idea/
+
+# Ruff stuff:
+.ruff_cache/
+
+# PyPI configuration file
+.pypirc

README.md

@@ -5,28 +5,28 @@ Smart dynamic swap management for Linux, written in Rust.
 ## Features
 
 - **Auto-detection**: Automatically chooses optimal swap strategy for your filesystem
-- **Zswap + SwapFC**: Compressed RAM cache with dynamic btrfs swap files
+- **Multi-filesystem**: Supports btrfs, ext4, and xfs for swap files
+- **Zswap + SwapFC**: Compressed RAM cache with dynamic swap files
 - **Zram + SwapFC**: Alternative mode with zram as primary swap
 - **Zram writeback**: Move idle pages from zram to disk (kernel 5.4+)
-- **Sparse files (thin provisioning)**: Swap files don't pre-allocate disk space
-- **Btrfs optimized**: Optional compression mode for swap data
+- **Fallback support**: Automatically falls back to zram-only if swap files fail
 - **Lightweight**: ~250 KB binary vs ~10 MB Python version
 
 ## Swap Modes
 
 | Mode | Description | Best For |
 |------|-------------|----------|
-| `auto` | Auto-detect: btrfs → zswap+swapfc, other → zram | Most users |
-| `zswap+swapfc` | Zswap cache + dynamic swap files | **Desktop (btrfs)** |
+| `auto` | Auto-detect: btrfs/ext4/xfs → zswap+swapfc, other → zram | Most users |
+| `zswap+swapfc` | Zswap cache + dynamic swap files | **Desktop** |
 | `zram+swapfc` | Zram primary + swap files overflow | Memory-constrained |
-| `zram` | Zram only (no disk swap) | Non-btrfs systems |
+| `zram` | Zram only (no disk swap) | Unsupported filesystems |
 | `manual` | Use explicit settings | Advanced users |
 
 ### How Each Mode Works
 
-**zswap + swapfc (default for btrfs)**:
+**zswap + swapfc (default for btrfs/ext4/xfs)**:
 - Zswap compresses pages in RAM before writing to swap
-- SwapFC creates swap files as sparse files (thin provisioning)
+- SwapFC creates pre-allocated swap files (512MB each)
 - Disk space is only used when zswap pool is full
 - Best desktop performance with efficient disk usage
 
@@ -113,12 +113,13 @@ swap_mode=auto
 
 ################################################################################
 # Zswap (used in zswap+swapfc mode)
+# Modern defaults for desktop Linux (kernel 6.x+)
 ################################################################################
-zswap_compressor=zstd            # lzo lz4 zstd lzo-rle lz4hc
-zswap_max_pool_percent=45        # Max % of RAM for pool
-zswap_zpool=zsmalloc             # Memory allocator
-zswap_shrinker_enabled=1         # Move cold pages to disk
-zswap_accept_threshold=80        # Accept threshold after pool full
+zswap_compressor=zstd            # lzo lz4 zstd lzo-rle lz4hc (zstd = best)
+zswap_max_pool_percent=45        # Max % of RAM for pool (20-50 typical)
+zswap_zpool=zsmalloc             # Memory allocator (default upstream)
+zswap_shrinker_enabled=1         # Evict cold pages to disk (default since 6.8)
+zswap_accept_threshold=90        # Accept threshold after pool full
 
 ################################################################################
 # Zram (used in zram modes)
@@ -141,12 +142,10 @@ swapfc_free_ram_perc=35          # Create when free RAM < this %
 swapfc_free_swap_perc=25         # Create more when free swap < this %
 swapfc_path=/swapfc/swapfile     # Path for swap files
 
-# Sparse files (thin provisioning) - ENABLED BY DEFAULT
-# Swap files appear full size but only allocate disk space when written.
-# Ideal with zswap: pages stay in RAM, disk is only used on writeback.
-# swapfc_use_sparse_disable=1    # Uncomment to pre-allocate disk space
+# Pre-allocated files (default) - more stable, no loop device needed
+swapfc_use_sparse=0              # 0=pre-allocate (default), 1=sparse
 
-# Btrfs compression mode (experimental)
+# Btrfs compression mode (experimental) and need use loop device
 swapfc_use_btrfs_compression=0   # Double compression: zswap + btrfs
 ```
 
@@ -174,21 +173,22 @@ zram_writeback_dev=/dev/sda5
 
 Requires kernel compiled with `CONFIG_ZRAM_WRITEBACK`.
 
-## Sparse Files (Thin Provisioning)
+## File Allocation Mode
 
-By default, swap files are created as sparse files:
+By default, swap files are **pre-allocated** using `fallocate`:
 
-- Files appear as 512M but start with 0 bytes on disk
-- Disk blocks are allocated only when data is actually written
-- With zswap, most pages stay compressed in RAM
-- Disk is only used when zswap pool is full (writeback)
+- Files reserve 512M on disk immediately
+- More stable under memory pressure (no loop device needed)
+- Better for most desktop and server workloads
 
-To disable and pre-allocate all disk space:
+To use sparse files (thin provisioning) instead:
 
 ```ini
-swapfc_use_sparse_disable=1
+swapfc_use_sparse=1
 ```
 
+Sparse mode creates files that only allocate disk space when written, but requires a loop device which can cause issues under extreme memory pressure.
+
 ## File Locations
 
 | Path | Description |

include/swap-default.conf

@@ -23,10 +23,10 @@ swap_mode=auto
 # Requires a backing swap device (swap file or partition).
 ################################################################################
 
-zswap_compressor=zstd            # lzo lz4 zstd lzo-rle lz4hc
-zswap_max_pool_percent=50        # Max % of RAM for compressed pool
-zswap_zpool=zsmalloc             # Memory allocator (zsmalloc better than zbud)
-zswap_shrinker_enabled=0         # Proactively move cold pages to swap
+zswap_compressor=zstd            # lzo lz4 zstd lzo-rle lz4hc (zstd = best balance)
+zswap_max_pool_percent=45        # Max % of RAM for compressed pool (20-50 typical)
+zswap_zpool=zsmalloc             # Memory allocator (zsmalloc = best, default upstream)
+zswap_shrinker_enabled=1         # Proactively evict cold pages to disk (default since 6.8)
 zswap_accept_threshold=90        # Accept pages again after pool was full (%)
 
 ################################################################################
@@ -50,14 +50,16 @@ zram_writeback_dev=         # Backing device (partition or empty for auto loop)
 zram_writeback_size=1G      # Size of auto-created backing file
 
 ################################################################################
-# SwapFC - Dynamic swap file management (btrfs only)
+# SwapFC - Dynamic swap file management
+# Supports: btrfs, ext4, xfs (auto-detected)
 # Used in zram+swapfc, zswap+swapfc modes, or manual with swapfc_enabled=1
 #
-# Creates swap files on-demand as memory pressure increases
+# Creates swap files on-demand as memory pressure increases.
+# If swap file creation fails, automatically falls back to zram-only mode.
 ################################################################################
 
 # swapfc_chunk_size supports: 1G, 512M, 10% (percentage of RAM)
-swapfc_chunk_size=20%            # Size of each swap file
+swapfc_chunk_size=512M           # Size of each swap file (512M = good balance)
 swapfc_max_count=32              # Maximum number of swap files
 swapfc_min_count=1               # Minimum (1 for zswap backing)
 swapfc_free_ram_perc=35          # Create swap when free RAM < this %
@@ -67,11 +69,11 @@ swapfc_priority=50               # Swap priority (decreases per file)
 swapfc_path=/swapfc/swapfile     # Path for swap files (must be btrfs)
 swapfc_frequency=1               # Check interval in seconds
 
-# Sparse files (thin provisioning) - ENABLED BY DEFAULT
-# Creates swap files that only allocate disk space when data is actually written.
-# This is ideal with zswap: pages stay in RAM until pool is full, then disk is used.
-# Uses loop device automatically (required for sparse swap files).
-# swapfc_use_sparse_disable=1    # Uncomment to pre-allocate disk space
+# File allocation mode:
+# - Pre-allocated (default): Uses fallocate, reserves disk space upfront, no loop device
+# - Sparse (thin): Uses truncate, only uses disk when written, requires loop device
+# Pre-allocated is more stable and avoids potential deadlocks under memory pressure.
+swapfc_use_sparse=0              # 0=pre-allocate (stable, default), 1=sparse (loop device)
 
 # Btrfs compression mode: uses loop device over sparse file on compressed btrfs
 # This enables swap data to be compressed on disk by btrfs (zstd)