Page Cache Calculator
Calculate the portion of RAM used as page cache and its effect on available memory.
About Page Cache Calculator
Page cache (the Cached field in /proc/meminfo, plus Buffers for block-device metadata) holds recently accessed file data in RAM so repeat reads avoid disk I/O entirely. It grows to fill whatever RAM isn't claimed by applications and shrinks automatically (least-recently-used pages evicted first) when applications need more memory — this is why a healthy Linux system typically shows most of its RAM as 'used' by cache, which is a feature, not a leak.
Formula
Page cache total
page_cache = Cached + Buffers
- C
- Cached (file page cache)
- B
- Buffers (block device buffers)
Worked example
With the default values below, Page Cache Calculator returns Total Page Cache (MB) of 6,300. Change any input above and every figure here is recalculated in your browser.
Inputs used
- MemTotal (MB)minimum 1
- 16,384
- Cached (MB, from /proc/meminfo)minimum 0
- 6,000
- Buffers (MB, from /proc/meminfo)minimum 0
- 300
- Application Working Set (GB)minimum 0
- 5
Results
- Total Page Cache (MB)
- 6,300
- Page Cache as % of RAM
- 38.45%
- Estimated Cache Hit Ratio
- 100.0%
- Note
- Page cache (Cached + Buffers) is reclaimable — it counts toward MemAvailable, not toward memory pressure.
Step by step
- 1Values used
- 2Page cache total
- 3Total Page Cache (MB)= 6,300
- 4Page Cache as % of RAM= 38.45
- 5Estimated Cache Hit Ratio= 100.0
- 6Note= Page cache (Cached + Buffers) is reclaimable — it counts toward MemAvailable, not toward memory pressure.
Assumptions and limits
- The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
What's the difference between page cache and a database's own cache?
Page cache operates at the OS/filesystem level and caches raw file blocks regardless of what reads them; a database's internal cache (e.g. PostgreSQL's shared_buffers or MySQL's InnoDB buffer pool) caches parsed, structured pages at the application level with knowledge of query patterns. Many systems benefit from both layers working together, though tuning them to avoid excessive double-caching is a common performance exercise.
Does page cache persist across reboots?
No — page cache lives entirely in volatile RAM and is lost on reboot or power loss, since it's just a performance optimization over data that already exists safely on disk, not a data store in its own right.
How can I check what's using page cache?
`free -h` shows the aggregate cache size, while tools like vmtouch or fincore can show which specific files currently have pages resident in cache, useful for verifying that a hot dataset is actually cache-resident as expected.