Provides information about distribution and utilization of memory. This varies by architecture and compile options. The following is from a 16GB PIII, which has highmem enabled. You may not have all of these fields. MemTotal: 16344972 kB MemFree: 13634064 kB MemAvailable: 14836172 kB Buffers: 3656 kB Cached: 1195708 kB SwapCached: 0 kB Active: 891636 kB Inactive: 1077224 kB HighTotal: 15597528 kB HighFree: 13629632 kB LowTotal: 747444 kB LowFree: 4432 kB SwapTotal: 0 kB SwapFree: 0 kB Dirty: 968 kB Writeback: 0 kB AnonPages: 861800 kB Mapped: 280372 kB Shmem: 644 kB KReclaimable: 168048 kB Slab: 284364 kB SReclaimable: 159856 kB SUnreclaim: 124508 kB PageTables: 24448 kB NFS_Unstable: 0 kB Bounce: 0 kB WritebackTmp: 0 kB CommitLimit: 7669796 kB Committed_AS: 100056 kB VmallocTotal: 112216 kB VmallocUsed: 428 kB VmallocChunk: 111088 kB Percpu: 62080 kB HardwareCorrupted: 0 kB AnonHugePages: 49152 kB ShmemHugePages: 0 kB ShmemPmdMapped: 0 kB MemTotal: Total usable ram (i.e. physical ram minus a few reserved bits and the kernel binary code) MemFree: The sum of LowFree+HighFree MemAvailable: An estimate of how much memory is available for starting new applications, without swapping. Calculated from MemFree, SReclaimable, the size of the file LRU lists, and the low watermarks in each zone. The estimate takes into account that the system needs some page cache to function well, and that not all reclaimable slab will be reclaimable, due to items being in use. The impact of those factors will vary from system to system. Buffers: Relatively temporary storage for raw disk blocks shouldn't get tremendously large (20MB or so) Cached: in-memory cache for files read from the disk (the pagecache). Doesn't include SwapCached SwapCached: Memory that once was swapped out, is swapped back in but still also is in the swapfile (if memory is needed it doesn't need to be swapped out AGAIN because it is already in the swapfile. This saves I/O) Active: Memory that has been used more recently and usually not reclaimed unless absolutely necessary. Inactive: Memory which has been less recently used. It is more eligible to be reclaimed for other purposes HighTotal: HighFree: Highmem is all memory above ~860MB of physical memory Highmem areas are for use by userspace programs, or for the pagecache. The kernel must use tricks to access this memory, making it slower to access than lowmem. LowTotal: LowFree: Lowmem is memory which can be used for everything that highmem can be used for, but it is also available for the kernel's use for its own data structures. Among many other things, it is where everything from the Slab is allocated. Bad things happen when you're out of lowmem. SwapTotal: total amount of swap space available SwapFree: Memory which has been evicted from RAM, and is temporarily on the disk Dirty: Memory which is waiting to get written back to the disk Writeback: Memory which is actively being written back to the disk AnonPages: Non-file backed pages mapped into userspace page tables HardwareCorrupted: The amount of RAM/memory in KB, the kernel identifies as corrupted. AnonHugePages: Non-file backed huge pages mapped into userspace page tables Mapped: files which have been mmaped, such as libraries Shmem: Total memory used by shared memory (shmem) and tmpfs ShmemHugePages: Memory used by shared memory (shmem) and tmpfs allocated with huge pages ShmemPmdMapped: Shared memory mapped into userspace with huge pages KReclaimable: Kernel allocations that the kernel will attempt to reclaim under memory pressure. Includes SReclaimable (below), and other direct allocations with a shrinker. Slab: in-kernel data structures cache SReclaimable: Part of Slab, that might be reclaimed, such as caches SUnreclaim: Part of Slab, that cannot be reclaimed on memory pressure PageTables: amount of memory dedicated to the lowest level of page tables. NFS_Unstable: NFS pages sent to the server, but not yet committed to stable storage Bounce: Memory used for block device "bounce buffers" WritebackTmp: Memory used by FUSE for temporary writeback buffers CommitLimit: Based on the overcommit ratio ('vm.overcommit_ratio'), this is the total amount of memory currently available to be allocated on the system. This limit is only adhered to if strict overcommit accounting is enabled (mode 2 in 'vm.overcommit_memory'). The CommitLimit is calculated with the following formula: CommitLimit = ([total RAM pages] - [total huge TLB pages]) * overcommit_ratio / 100 + [total swap pages] For example, on a system with 1G of physical RAM and 7G of swap with a `vm.overcommit_ratio` of 30 it would yield a CommitLimit of 7.3G. For more details, see the memory overcommit documentation in vm/overcommit-accounting. Committed_AS: The amount of memory presently allocated on the system. The committed memory is a sum of all of the memory which has been allocated by processes, even if it has not been "used" by them as of yet. A process which malloc()'s 1G of memory, but only touches 300M of it will show up as using 1G. This 1G is memory which has been "committed" to by the VM and can be used at any time by the allocating application. With strict overcommit enabled on the system (mode 2 in 'vm.overcommit_memory'),allocations which would exceed the CommitLimit (detailed above) will not be permitted. This is useful if one needs to guarantee that processes will not fail due to lack of memory once that memory has been successfully allocated. VmallocTotal: total size of vmalloc memory area VmallocUsed: amount of vmalloc area which is used VmallocChunk: largest contiguous block of vmalloc area which is free Percpu: Memory allocated to the percpu allocator used to back percpu allocations. This stat excludes the cost of metadata.
