From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with ESMTP id 7ACF06B004F for ; Tue, 7 Jul 2009 15:51:07 -0400 (EDT) MIME-Version: 1.0 Message-ID: <92d23660-c8a3-4107-aee6-ec251ff65b99@default> Date: Tue, 7 Jul 2009 12:53:06 -0700 (PDT) From: Dan Magenheimer Subject: RE: [RFC PATCH 0/4] (Take 2): transcendent memory ("tmem") for Linux In-Reply-To: <4A5385AD.9000800@redhat.com> Content-Type: text/plain; charset=Windows-1252 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org To: Rik van Riel Cc: linux-kernel@vger.kernel.org, npiggin@suse.de, akpm@osdl.org, jeremy@goop.org, xen-devel@lists.xensource.com, tmem-devel@oss.oracle.com, alan@lxorguk.ukuu.org.uk, linux-mm@kvack.org, kurt.hackel@oracle.com, Rusty Russell , dave.mccracken@oracle.com, Marcelo Tosatti , sunil.mushran@oracle.com, Avi Kivity , Schwidefsky , chris.mason@oracle.com, Balbir Singh List-ID: > From: Rik van Riel [mailto:riel@redhat.com] > Dan Magenheimer wrote: > > "Preswap" IS persistent, but for various reasons may not always be > > available for use, again due to factors that may not be=20 > visible to the > > kernel (but, briefly, if the kernel is being "good" and has=20 > shared its > > resources nicely, then it will be able to use preswap, else=20 > it will not). > > Once a page is put, a get on the page will always succeed.=20 >=20 > What happens when all of the free memory on a system > has been consumed by preswap by a few guests? > Will the system be unable to start another guest, The default policy (and only policy implemented as of now) is that no guest is allowed to use more than max_mem for the sum of directly-addressable memory (e.g. RAM) and persistent tmem (e.g. preswap). So if a guest is using its default memory=3D=3Dmax_mem and is doing no ballooning, nothing can be put in preswap by that guest. =20 > or is there some way to free the preswap memory? Yes and no. There is no way externally to free preswap memory, but an in-guest userland root service can write to sysfs to affect preswap size. This essentially does a partial swapoff on preswap if there is sufficient (directly addressable) guest RAM available. (I have this prototyped as part of the xenballoond self-ballooning service in xen-unstable.) 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