Page Cache Utilities

Small Linux utilities for managing the page cache. Useful for cold-cache benchmarking, I/O investigation, and anything that needs to know or control what the kernel has cached from disk.

Tools

• duncache: evict files or directory trees from the page cache using posix_fadvise(..., POSIX_FADV_DONTNEED).
• incache: report how many pages of a file (or tree) are resident in the page cache, using mincore().

Build

make

Usage

duncache [-q] [--no-sync] <path>...
incache  [-q] [-j|--json]  <path>...

duncache

-q, --quiet      no output unless an error occurs
    --no-sync    skip fdatasync() before eviction

Exits 0 if every path was evicted, 1 if any failed.

incache

-q, --quiet      no output; exit code only
-j, --json       one json object per path

Reports cached/total pages (percent). Exits 0 if every path is fully cached, 1 if any path is partially or not cached, 2 on error.

Example

# create a 1 MiB test file
dd if=/dev/urandom of=testfile bs=1M count=1

# read it so the kernel caches it
cat testfile > /dev/null

# check residency
./incache testfile
# testfile	256/256 pages (100.0%)

# evict
./duncache testfile
# testfile -> POSIX_FADV_DONTNEED

# check again
./incache testfile
# testfile	0/256 pages (0.0%)

# scriptable use
if ./incache -q testfile; then
    echo "fully cached"
else
    echo "not (fully) cached"
fi