Re: [RFC PATCH -mm] provide estimated available memory in /proc/meminfo

[Andrew Morton <akpm@linux-foundation.org>]

On Tue, 5 Nov 2013 17:38:52 -0500 Rik van Riel <riel@redhat.com> wrote:

> 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.
> 

That's a good idea.

>  fs/proc/meminfo.c | 36 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 36 insertions(+)

Documentation/filesystems/proc.txt told me it's feeling all offended.