linux-kernel - Re: [PATCH] mmu_notifier, kvm: Introduce dirty bit tracking in spte and mmu notifier to help KSM dirty bit tracking

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]

Message-ID: <4E028215.90107@redhat.com>
Date:	Wed, 22 Jun 2011 20:00:21 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Nai Xia <nai.xia@...il.com>
CC:	Andrea Arcangeli <aarcange@...hat.com>,
	Izik Eidus <izik.eidus@...ellosystems.com>,
	Avi Kivity <avi@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>,
	Chris Wright <chrisw@...s-sol.org>,
	linux-mm <linux-mm@...ck.org>,
	Johannes Weiner <hannes@...xchg.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	kvm <kvm@...r.kernel.org>
Subject: Re: [PATCH] mmu_notifier, kvm: Introduce dirty bit tracking in spte
 and mmu notifier to help KSM dirty bit tracking

On 06/22/2011 07:37 PM, Nai Xia wrote:

> On 2MB pages, I'd like to remind you and Rik that ksmd currently splits
> huge pages before their sub pages gets really merged to stable tree.

Your proposal appears to add a condition that causes ksmd to skip
doing that, which can cause the system to start using swap instead
of sharing memory.

> So when there are many 2MB pages each having a 4kB subpage
> changed for all time, this is already a concern for ksmd to judge
> if it's worthwhile to split 2MB page and get its sub-pages merged.
> I think the policy for ksmd in a system should be "If you cannot do sth good,
> at least do nothing evil". So I really don't think we can satisfy _all_ people.
> Get a general method and give users one or two knobs to tune it when they
> are the corner cases. How do  you think of my proposal ?

I think your proposal makes sense for 4kB pages, but the ksmd
policy for 2MB pages probably needs to be much more aggressive.

-- 
All rights reversed
--
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/