The subtraction was marked as reinforcing the misconception,
that memory in the page cache can be considered free.
The Cached value is not a sum of page cache and tmpfs,
as the tmpfs memory lives in the page cache and therefore
it's an inseparable part of it.
tmpfs has become much more widely used since distributions use it for
/tmp (Fedora 18+). In /proc/meminfo, memory used by tmpfs is accounted
into "Cached" (aka "NR_FILE_PAGES",
http://lxr.free-electrons.com/source/mm/shmem.c#L301 ).
The tools just pass it on, so what top, free and vmstat report as
"cached" is the sum of page cache and tmpfs.
free has the extremely useful "-/+ buffers/cache" output. However, now
that tmpfs is accounted into "cached", those numbers are way off once
you have big files in /tmp.
Fortunately, kernel 2.6.32 introduces "Shmem", which makes tmpfs memory
usage accessible from userspace (
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=4b02108ac1b3354a22b0d83c684797692efdc395 ).
This patch substracts Shmem from Cached to get the actual page cache
memory. This makes both issues mentioned above disappear. For older
kernels, Shmem is not available (hence zero) and this patch is no-op.
Additionally:
* Update the man pages of free and vmstat to explain what is happening
* Finally drop "MemShared" from the /proc/meminfo parser, it has been
dead for 10+ years and is only causing confusion ( removed in kernel
2.5.54, see
https://git.kernel.org/cgit/linux/kernel/git/tglx/history.git/commit/?id=fe04e9451e5a159247cf9f03c615a4273ac0c571 )
From now the vmstat can append a timestamp to each line in the
VMSTAT and DISKSTAT mode. You can achieve that with the '-t'
switch.
The '-w' switch now works in the DISKSTAT mode too.
This is a rework of the merge request #5 that unconditionally
forced the output to cross the 80 chars border.
With this commit users can switch to the wide output mode
with the -w option.
All warnings where about unnecessary quoting. The scriptlet
below will tell what was wrong.
for I in ./top/top.1 ./ps/ps.1 ./*.[0-9]; do
echo "== $I warnings =="
man --warnings=all $I > /dev/null
done
This should probably be turned to 'make check' script.
Signed-off-by: Sami Kerola <kerolasa@iki.fi>
