linux-kernel - Re: [PATCH V3] KSM: allow dedup all tasks memory

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, 13 Nov 2018 22:53:34 +0000
From:   Pavel Tatashin <pasha.tatashin@...een.com>
To:     Timofey Titovets <timofey.titovets@...esis.ru>
Cc:     Oleksandr Natalenko <oleksandr@...alenko.name>,
        Jann Horn <jannh@...gle.com>, linux-doc@...r.kernel.org,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        linux-mm@...ck.org, Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH V3] KSM: allow dedup all tasks memory

> > > 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.
> 
> With all due respect to you, for that type of things we need
> mm maintainer opinion.

As far as I understood, you already got directions from the maintainers
to do similar to the way THP is implemented, and THP uses two flags:

VM_HUGEPAGE VM_NOHUGEPAGE, the same as I am thinking ksm should do if we
honor MADV_UNMERGEABLE.

When VM_NOHUGEPAGE is set khugepaged ignores those VMAs.

There may be a way to add VM_UNMERGEABLE without extending the size of
vm_flags, but that would be a good start point in looking how to add a
new flag.

Again, you could simply enable this feature on 64-bit only.

Pasha