From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx145.postini.com [74.125.245.145]) by kanga.kvack.org (Postfix) with SMTP id 4AF066B000C for ; Tue, 22 Jan 2013 18:59:20 -0500 (EST) MIME-Version: 1.0 Message-ID: <6dc259d4-440e-4926-bf5f-e9deb9a19f09@default> Date: Tue, 22 Jan 2013 15:58:53 -0800 (PST) From: Dan Magenheimer Subject: High slab usage testing with zcache/zswap (Was: [PATCH 7/8] zswap: add to mm/) References: <1355262966-15281-1-git-send-email-sjenning@linux.vnet.ibm.com> <1355262966-15281-8-git-send-email-sjenning@linux.vnet.ibm.com> <0e91c1e5-7a62-4b89-9473-09fff384a334@default> <50E32255.60901@linux.vnet.ibm.com> <50E4588E.6080001@linux.vnet.ibm.com> <28a63847-7659-44c4-9c33-87f5d50b2ea0@default> <50E479AD.9030502@linux.vnet.ibm.com> <9955b9e0-731b-4cbf-9db0-683fcd32f944@default> <20130103073339.GF3120@dastard> In-Reply-To: <20130103073339.GF3120@dastard> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: Dave Chinner Cc: Seth Jennings , Konrad Wilk , linux-mm@kvack.org, linux-kernel@vger.kernel.org > From: Dave Chinner [mailto:david@fromorbit.com] > Sent: Thursday, January 03, 2013 12:34 AM > Subject: Re: [PATCH 7/8] zswap: add to mm/ >=20 > > > On 01/02/2013 09:26 AM, Dan Magenheimer wrote: > > > > However if one compares the total percentage > > > > of RAM used for zpages by zswap vs the total percentage of RAM > > > > used by slab, I suspect that the zswap number will dominate, > > > > perhaps because zswap is storing primarily data and slab is > > > > storing primarily metadata? > > > > > > That's *obviously* 100% dependent on how you configure zswap. But, t= hat > > > said, most of _my_ systems tend to sit with about 5% of memory in > > > reclaimable slab > > > > The 5% "sitting" number for slab is somewhat interesting, but > > IMHO irrelevant here. The really interesting value is what percent > > is used by slab when the system is under high memory pressure; I'd > > imagine that number would be much smaller. True? >=20 > Not at all. The amount of slab memory used is wholly dependent on > workload. I have plenty of workloads with severe memory pressure > that I test with that sit at a steady state of >80% of ram in slab > caches. These workloads are filesytem metadata intensive rather than > data intensive, that's exactly the right cache balance for the > system to have.... Hey Dave -- I'd like to do some zcache policy testing where the severe memory pressure is a result of something like the above where >80% of ram is in slab caches. Any thoughts on how to do this or easily simulate it on a very simple hardware system (e.g. PC with one SATA disk)? Or is a "big data" configuration required? Thanks for any advice! Dan -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org