From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk1-f199.google.com (mail-qk1-f199.google.com [209.85.222.199]) by kanga.kvack.org (Postfix) with ESMTP id 6E1D26B0003 for ; Tue, 13 Nov 2018 14:16:58 -0500 (EST) Received: by mail-qk1-f199.google.com with SMTP id x125so15196910qka.17 for ; Tue, 13 Nov 2018 11:16:58 -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 w20sor3128834qtn.69.2018.11.13.11.16.57 for (Google Transport Security); Tue, 13 Nov 2018 11:16:57 -0800 (PST) Date: Tue, 13 Nov 2018 19:16:53 +0000 From: Pavel Tatashin Subject: Re: [PATCH V3] KSM: allow dedup all tasks memory Message-ID: <20181113191653.btbzobquxtwt47z4@soleen.tm1wkky2jk1uhgkn0ivaxijq1c.bx.internal.cloudapp.net> References: <20181113175930.3g65rlhbaimstq7g@soleen.tm1wkky2jk1uhgkn0ivaxijq1c.bx.internal.cloudapp.net> <20181113183510.5y2hzruoi23e7o2t@soleen.tm1wkky2jk1uhgkn0ivaxijq1c.bx.internal.cloudapp.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Timofey Titovets Cc: Oleksandr Natalenko , Jann Horn , linux-doc@vger.kernel.org, Linux Kernel , linux-mm@kvack.org, Matthew Wilcox On 18-11-13 21:54:13, Timofey Titovets wrote: > D2N?, 13 D 1/2 D 3/4 N?D+-. 2018 D3. D2 21:35, Pavel Tatashin : > > > > On 18-11-13 21:17:42, Timofey Titovets wrote: > > > D2N?, 13 D 1/2 D 3/4 N?D+-. 2018 D3. D2 20:59, Pavel Tatashin : > > > > > > > > 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. > > > > > > > > > > We just did not have VM/Madvise flag for that currently. > > > Same as THP. > > > Because all logic written with assumption, what we have exactly 2 states. > > > Allow/Disallow (More like not allow). > > > > > > And if we try to add, that must be something like: > > > MADV_FORBID_* to disallow something completely. > > > > No need to add new user flag MADV_FORBID, we should keep MADV_MERGEABLE > > and MADV_UNMERGEABLE, but make them work so when MADV_UNMERGEABLE is > > set, memory is indeed becomes always unmergeable regardless of ksm mode > > of operation. > > > > To do the above in ksm_madvise(), a new state should be added, for example > > instead of: > > > > case MADV_UNMERGEABLE: > > *vm_flags &= ~VM_MERGEABLE; > > > > A new flag should be used: > > *vm_flags |= VM_UNMERGEABLE; > > > > I think, without honoring MADV_UNMERGEABLE correctly, this patch won't > > be accepted. > > > > Pasha > > > > That must work, but we out of bit space in vm_flags [1]. > i.e. first 32 bits already defined, and other only accessible only on > 64-bit machines. So, grow vm_flags_t to 64-bit, or enable this feature on 64-bit only. > > 1. https://elixir.bootlin.com/linux/latest/source/include/linux/mm.h#L219