Page Cache
Also known as: os page cache, filesystem cache memory, page cache
The page cache is the operating system's in-RAM copy of recently read or written file data. It lets repeat file access hit memory instead of slow storage, and it is reclaimed automatically the moment apps need RAM — so it is not 'used up' memory or app cache.
- The page cache is an in-RAM mirror of recently used file data, managed automatically by the OS.
- It's reclaimable: the kernel drops clean cached pages instantly when an app needs memory.
- Unlike app cache, it never counts toward used storage and frees itself on reboot — no manual cleanup needed.
What the page cache does
When a program reads a file, the kernel copies those disk blocks into RAM and keeps them in the page cache. The next read of the same data is served from memory at a fraction of the latency of going to flash storage. Writes work the same way: data lands in the page cache first (a 'dirty' page) and is flushed to disk later, which is why an unexpected power loss can lose very recent writes.
This caching is automatic and OS-managed — apps don't allocate it explicitly. On Linux-based Android, the page cache is a core part of the memory manager. On iOS/macOS the unified buffer cache plays the same role. Because it is opportunistic, a healthy system tends to keep most 'free' RAM filled with cached file pages; that is the OS working as intended, not a leak.
Page cache vs app cache vs RAM
These are easy to confuse. The page cache lives in RAM and is a temporary mirror of file contents; it disappears on reboot and is never counted against your storage. App cache (the getCacheDir / NSCachesDirectory kind) is files written to persistent storage that count toward your device's used space and show up under Settings > Storage. Clearing app cache frees disk; the page cache frees itself.
Crucially, the kernel treats the page cache as reclaimable: if an app needs more memory, the OS instantly drops clean cached pages to make room (writing back dirty ones first). That's why tools and dashboards that show RAM 'almost full' are usually counting cache — true available memory includes everything the page cache can give back on demand.
Why it matters for cleanup
The page cache is one of the biggest reasons 'RAM cleaner' actions are mostly theater: forcibly emptying it just makes the OS re-read files from storage and slows the next launch, while the kernel would have reclaimed that memory automatically if it were ever needed. There is nothing on disk to recover by touching it.
Real storage wins come from the persistent side, not RAM: clearing app cache, removing junk files, and deleting duplicate photos and large media. Cleanor focuses there — on data that actually occupies your storage — and leaves the page cache to the OS, which manages it far better than any manual purge could.