From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keir Fraser Subject: Re: [Xen-devel] Re: Max. PV and HVM Guests Date: Mon, 09 Nov 2009 15:24:59 +0000 Message-ID: References: <20091109151750.GN16033@reaktio.net> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <20091109151750.GN16033@reaktio.net> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-users-bounces@lists.xensource.com Errors-To: xen-users-bounces@lists.xensource.com To: Pasi =?ISO-8859-1?B?S+Rya2vkaW5lbg==?= , Nick Couchman Cc: "xen-devel@lists.xensource.com" , "Mr. Teo En Ming (Zhang Enming)" , "xen-users@lists.xensource.com" , Robert Dunkley List-Id: xen-devel@lists.xenproject.org On 09/11/2009 15:17, "Pasi K=E4rkk=E4inen" wrote: >> Furthermore, while I'm not >> Linux developer and so not familiar with how Linux calculates buffering >> and caching, I do know that my Linux systems dynamically manage buffers >> and caches, and when memory is reduced or some application requires a >> larger amount of physical memory, Linux reduces the amount of data in >> buffers and caches. >>=20 >=20 > Yeah, it has to do with sizing the network buffers, caches etc.. >=20 > It shouldn't _crash_, so Teo is seeing some bug I believe. But it has > always been "best practice" to limit dom0 memory - and prevent weird > things happening later (like "memory squeeze in netback driver"). The issue is not really kernel data like network buffers and buffer cache. It is kernel memory metadata -- primarily the per-page info structure that the kernel maintains. The metadata doesn't get shrunk with memory size when ballooning out, hence it increases as a proportion of memory still assigned to the domain. That really is significant when aggressively ballooning down a large-memory domain. -- Keir