From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk1-f197.google.com (mail-qk1-f197.google.com [209.85.222.197]) by kanga.kvack.org (Postfix) with ESMTP id 81E0B6B0007 for ; Tue, 13 Nov 2018 12:59:35 -0500 (EST) Received: by mail-qk1-f197.google.com with SMTP id s19so32224986qke.20 for ; Tue, 13 Nov 2018 09:59:35 -0800 (PST) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id v7sor13902018qvl.52.2018.11.13.09.59.33 for (Google Transport Security); Tue, 13 Nov 2018 09:59:33 -0800 (PST) Date: Tue, 13 Nov 2018 17:59:30 +0000 From: Pavel Tatashin Subject: Re: [PATCH V3] KSM: allow dedup all tasks memory Message-ID: <20181113175930.3g65rlhbaimstq7g@soleen.tm1wkky2jk1uhgkn0ivaxijq1c.bx.internal.cloudapp.net> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Oleksandr Natalenko Cc: jannh@google.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, timofey.titovets@synesis.ru, willy@infradead.org On 18-11-13 15:23:50, Oleksandr Natalenko wrote: > Hi. > > > Yep. However, so far, it requires an application to explicitly opt in > > to this behavior, so it's not all that bad. Your patch would remove > > the requirement for application opt-in, which, in my opinion, makes > > this way worse and reduces the number of applications for which this > > is acceptable. > > The default is to maintain the old behaviour, so unless the explicit > decision is made by the administrator, no extra risk is imposed. The new interface would be more tolerable if it honored MADV_UNMERGEABLE: KSM default on: merge everything except when MADV_UNMERGEABLE is excplicitly set. KSM default off: merge only when MADV_MERGEABLE is set. The proposed change won't honor MADV_UNMERGEABLE, meaning that application programmers won't have a way to prevent sensitive data to be every merged. So, I think, we should keep allow an explicit opt-out option for applications. > > > As far as I know, basically nobody is using KSM at this point. There > > are blog posts from several cloud providers about these security risks > > that explicitly state that they're not using memory deduplication. > > I tend to disagree here. Based on both what my company does and what UKSM > users do, memory dedup is a desired option (note "option" word here, not the > default choice). Lightweight containers is a use case for KSM: when many VMs share the same small kernel. KSM is used in production by large cloud vendors. Thank you, Pasha