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

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Date:	Wed, 6 Nov 2013 00:39:06 +0200
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Rik van Riel <riel@...hat.com>
Cc:	Ron van der Wees <rvdwees@...hat.com>,
	Erik Mouw <erik.mouw_2@....com>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	walken@...gle.com, Shaohua Li <shli@...nel.org>,
	Mel Gorman <mgorman@...e.de>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [RFC PATCH -mm] provide estimated available memory in
 /proc/meminfo

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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