linux-kernel - Re: computing drop-able caches

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Message-ID: <56BB7BC7.4040403@cisco.com>
Date:	Wed, 10 Feb 2016 10:04:55 -0800
From:	Daniel Walker <danielwa@...co.com>
To:	"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 02/08/2016 12:57 PM, Khalid Mughal (khalidm) wrote:
> How do we explain the discrepancy between MemAvaiable and MemFree count
> after we drop cache? In following output, which one represents correct
> data?
>
> [Linux_0:/]$ cat /proc/meminfo
> MemTotal:        3977836 kB
> MemFree:          747832 kB
> MemAvailable:    1441736 kB
> Buffers:          123976 kB
> Cached:          1210272 kB
> Active:          2496932 kB
> Inactive:         585364 kB
> Active(anon):    2243932 kB
> Inactive(anon):   142676 kB
> Active(file):     253000 kB
> Inactive(file):   442688 kB
> Dirty:                44 kB
> AnonPages:       1748088 kB
> Mapped:           406512 kB
> Shmem:            638564 kB
> Slab:              65656 kB
> SReclaimable:      30120 kB
> SUnreclaim:        35536 kB
> KernelStack:        5920 kB
> PageTables:        19040 kB
> CommitLimit:     1988916 kB
> Committed_AS:    3765252 kB
>
> [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.

Daniel