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

From: Kirill A. Shutemov
Date: Tue Nov 05 2013 - 18:35:42 EST

On Tue, Nov 05, 2013 at 05:38:52PM -0500, Rik van Riel 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.

ramfs pages first go to (in)active lists, moves to unevictable later, so
it's not really true already. ;)

Kirill A. Shutemov
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