[kernelreadfans] mem info
- From: mingz <mingz@xxxxxxxxxxx>
- To: kernelreadfans@xxxxxxxxxxxxx
- Date: Wed, 28 May 2003 22:06:45 -0400
from Dave Hansen's post
meminfo:
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.
> cat /proc/meminfo
MemTotal: 16344972 kB
MemFree: 13634064 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
Mapped: 280372 kB
Slab: 684068 kB
Committed_AS: 1576424 kB
PageTables: 24448 kB
ReverseMaps: 1080904
VmallocTotal: 112216 kB
VmallocUsed: 428 kB
VmallocChunk: 111088 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
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 availble 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
Mapped: files which have been mmaped, such as libraries
Slab: in-kernel data structures cache
Committed_AS: An estimate of how much RAM you would need to make a
99.99% guarantee that there never is OOM (out of memory)
for this workload. Normally the kernel will overcommit
memory. That means, say you do a 1GB malloc, nothing
happens, really. Only when you start USING that malloc
memory you will get real memory on demand, and just as
much as you use. So you sort of take a mortgage and hope
the bank doesn't go bust. Other cases might include when
you mmap a file that's shared only when you write to it
and you get a private copy of that data. While it normally
is shared between processes. The Committed_AS is a
guesstimate of how much RAM/swap you would need
worst-case.
PageTables: amount of memory dedicated to the lowest level of page
tables.
ReverseMaps: number of reverse mappings performed
VmallocTotal: total size of vmalloc memory area
VmallocUsed: amount of vmalloc area which is used
VmallocChunk: largest contigious block of vmalloc area which is free
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