linux-kernel - RE: [RFC PATCH 0/4] (Take 2): transcendent memory ("tmem") for Linux

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 7 Jul 2009 12:53:06 -0700 (PDT)
From:	Dan Magenheimer <dan.magenheimer@...cle.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	linux-kernel@...r.kernel.org, npiggin@...e.de, akpm@...l.org,
	jeremy@...p.org, xen-devel@...ts.xensource.com,
	tmem-devel@....oracle.com, alan@...rguk.ukuu.org.uk,
	linux-mm@...ck.org, kurt.hackel@...cle.com,
	Rusty Russell <rusty@...tcorp.com.au>,
	dave.mccracken@...cle.com, Marcelo Tosatti <mtosatti@...hat.com>,
	sunil.mushran@...cle.com, Avi Kivity <avi@...hat.com>,
	Schwidefsky <schwidefsky@...ibm.com>, chris.mason@...cle.com,
	Balbir Singh <balbir@...ux.vnet.ibm.com>
Subject: RE: [RFC PATCH 0/4] (Take 2): transcendent memory ("tmem") for Linux

> From: Rik van Riel [mailto:riel@...hat.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 
> visible to the
> > kernel (but, briefly, if the kernel is being "good" and has 
> shared its
> > resources nicely, then it will be able to use preswap, else 
> it will not).
> > Once a page is put, a get on the page will always succeed. 
> 
> 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==max_mem and is doing no ballooning, nothing can
be put in preswap by that guest.
 
> 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 from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/