# `memory`

Memory use, sampled once a second while a reader is visible. While
none is but a `graph` keeps history of it, it samples at the coarser
of that and a twentieth of the graph's `history` (at least 2 s);
otherwise not at all.

| Field | Type | |
| --- | --- | --- |
| `usage` | `float` | The fraction in use, 0 to 1. |
| `used` | `float` | Memory in use, in bytes (installed memory less what is available). |
| `total` | `float` | Memory installed, in bytes. |
| `available` | `float` | Memory available to start new programs without swapping, in bytes (the kernel's estimate, `MemAvailable`): free memory plus the cache it can drop. |
| `free` | `float` | Memory holding nothing at all, in bytes (`MemFree`): far less than `available`, since the kernel fills spare memory with cache. |
| `cached` | `float` | The page cache and buffers, in bytes (`Cached` plus `Buffers`): files kept in memory, most of it given back when programs need it. |
| `swap_used` | `float` | Swap in use, in bytes (`SwapTotal` less `SwapFree`). |
| `swap_total` | `float` | Swap configured, in bytes; 0 without swap. |