This is interesting:
This is interesting:
/proc/meminfo: provide estimated available memory
Many load balancing and workload placing programs check /proc/meminfo to
estimate how much free memory is available. They generally do this by
adding up "free" and "cached", which was fine ten years ago, but is
pretty much guaranteed to be wrong today.
It is wrong because Cached includes memory that is not freeable as page
cache, for example shared memory segments, tmpfs, and ramfs, and it does
not include reclaimable slab memory, which can take up a large fraction
of system memory on mostly idle systems with lots of files.
Currently, the amount of memory that is available for a new workload,
without pushing the system into swap, can be estimated from MemFree,
Active(file), Inactive(file), and SReclaimable, as well as the "low"
watermarks from /proc/zoneinfo.
However, this may change in the future, and user space really should not
be expected to know kernel internals to come up with an estimate for the
amount of free memory.
It is more convenient to provide such an estimate in /proc/meminfo. If
things change in the future, we only have to change it in one place.
Signed-off-by: Rik van Riel <riel@xxxxxxxxxx>
Reported-by: Erik Mouw <erik.mouw_2@xxxxxxx>
Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
On Wed, Dec 5, 2018 at 4:44 PM kyle Hailey <kylelf@xxxxxxxxx> wrote:
One of those questions that seems like it should have been nailed down 20
years ago but it still seems lack a clear answer
How do you detect memory issues ?
I always used "*po" or "paged outs*". Now on Amazon Linux I don't see
"po" but there is "bo" (blocks written out). In past, at least on OSF &
Ultrix, page outs were a sign of needed memory that was written out to disk
and when I needed that memory it would take a big performance hit to read
it in. Thus "po" was a good canary on the coal mine. Any consistent values
over over say 10 were a sign.
Some people use "*scan rate*" but I never found that as easy to interpret
as page outs. Again what values would you use
Some suggest using freeable memory as a yardstick where freeable is
"free" + "cached" or MemFree + Cached + Inactive. Even in this case what
would you use for values to alert on?
I've always ignored swap stats as if you are swapping it is too late.
What do you use to detect memory issues ?