linux-kernel - Re: computing drop-able caches

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Date:	Wed, 10 Feb 2016 11:11:26 -0800
From:	Daniel Walker <danielwa@...co.com>
To:	Dave Hansen <dave.hansen@...el.com>,
	"Khalid Mughal (khalidm)" <khalidm@...co.com>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>
Cc:	Alexander Viro <viro@...iv.linux.org.uk>,
	Michal Hocko <mhocko@...e.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"xe-kernel@...ernal.cisco.com" <xe-kernel@...ernal.cisco.com>
Subject: Re: computing drop-able caches

On 02/10/2016 10:13 AM, Dave Hansen wrote:
> On 02/10/2016 10:04 AM, Daniel Walker wrote:
>>> [Linux_0:/]$ echo 3 > /proc/sys/vm/drop_caches
>>> [Linux_0:/]$ cat /proc/meminfo
>>> MemTotal:        3977836 kB
>>> MemFree:         1095012 kB
>>> MemAvailable:    1434148 kB
>> I suspect MemAvailable takes into account more than just the droppable
>> caches. For instance, reclaimable slab is included, but I don't think
>> drop_caches drops that part.
> There's a bit for page cache and a bit for slab, see:
>
> 	https://kernel.org/doc/Documentation/sysctl/vm.txt
>
>

Ok, then this looks like a defect then. I would think MemAvailable would 
always be smaller then MemFree (after echo 3 > 
/proc/sys/vm/drop_caches).. Unless there is something else be accounted 
for that we aren't aware of.

Daniel